al-Salamu `Aleykum,
I would like to say, that the claim that every prophet appointed a successor and that there was no time unless Allah has an appointed Hujjah on earth, this is what is actually "bogus", not the other way.
To prove this to you, I say that we read in the Qur'an that there were prophets whose people disobeyed them, so Allah destroyed those entire nations and never left a trace of them, no successors were appointed.
The Qur'an has many examples of these folks, such as:
{We destroyed the generations before you when they did wrong; and their messengers (from Allah) came unto them with clear proofs (of His Sovereignty) but they would not believe. Thus do We reward the guilty folk.} [10:13]
{And Noah's folk, when they denied the messengers, We drowned them and made of them a portent for mankind. We have prepared a painful doom for evil-doers. - And (the tribes of) A'ad and Thamud, and the dwellers in Ar-Rass, and many generations in between.} [25:37-38]
There are also prophets like `Isa ibn Mariyam (as), he passed on and nobody succeeded him, and Allah asks him in the Qur'an:
{And when Allah saith: O Jesus, son of Mary! Didst thou say unto mankind: Take me and my mother for two gods beside Allah? he saith: Be glorified! It was not mine to utter that to which I had no right. If I used to say it, then Thou knewest it. Thou knowest what is in my mind, and I know not what is in Thy Mind. Lo! Thou, only Thou, art the Knower of Things Hidden? - I spoke unto them only that which Thou commandedst me, (saying): Worship Allah, my Lord and your Lord. I was a witness of them while I dwelt among them, and when Thou tookest me Thou wast the Watcher over them. Thou art Witness over all things.} [5:116-117]
If `Isa (as) had a successor then it is not right that Allah should ask him this, if the people after `Isa (as) took him as their Lord then it is the responsibility of his successor as he was the one in charge after him, so when `Isa (as) says that Allah was the witness after him, it means that there was no other individual present otherwise `Isa (as) would respond by saying: "Ask my successor which you have appointed, when I passed away they were no longer my responsibility but they became the responsibility of my successor."
The same can be said about prophet Ibrahim (as), he used to sit and contemplate and ponder on who God was, then he realized that God cannot be a planet or a star, God is the creator of everything, yet Ibrahim (as) did not learn this information from a successor before him, no such thing was written anywhere.
Prophet Muhammad (saw), Allah wrote in his book that he guided him and he taught him the book and the wisdom, Muhammad (saw) did not learn this from a successor before him nor was such a successor mentioned.
{Allah verily hath shown grace to the believers by sending unto them a messenger of their own who reciteth unto them His revelations, and causeth them to grow, and teacheth them the Scripture and wisdom; although before (he came to them) they were in flagrant error.} [3:164]
I say, this verse shows clearly that they were in a state of ignorance and misguidance before his coming, so does this include the successor which you claim was before him and his followers? If there was a successor would he not have done the same thing Muhammad (saw) did by teaching them the wisdom that they may be guided? How could they be in "flagrant error" if they had successors who were infallible and divinely appointed?
Allah (swt) clearly says that there was nobody before our Prophet (saw) of this nature:
{O People of the Scripture! Now hath Our messenger come unto you to make things plain unto you after an interval (of cessation) of the messengers, lest ye should say: There came not unto us a messenger of cheer nor any warner. Now hath a messenger of cheer and a warner come unto you. Allah is Able to do all things.} [5:19]
And he says:
{And thou was not beside the Mount when We did call; but (the knowledge of it is) a mercy from thy Lord that thou mayst warn a folk unto whom no warner came before thee, that haply they may give heed.} [28:46]
Notice that Allah is saying that there were no warners and guides before him to clarify the religion to the people, if there were prophets before him who succeeded `Isa (as) then Allah would not have said this. On the other hand, if each of the countless prophets and messengers had appointed a successor, and no time was devoid of a Hujjah, then there was no need to send Muhammad (saw) as a warner and a guide because each of the towns and the cities would have a man among them, infallible and divinely appointed, to lead the people to the truth and renew their religion.
From these verses and others like them, we understand that there was no one in his time who was upon Allah's true guidance, neither a messenger nor a prophet nor a successor, until Allah sent his servant Muhammad (saw) with the light. However, you claim that there were successors, and these successors inherited the knowledge of the prophets, so how can then Allah describe them as being in a state of misguidance and error?
Now that I spoke briefly on Wasiyyah, I move to your next point that is the need to appoint leaders.
You said how can the Prophet (saw) pass away without clarifying the matter of leadership?
I say he clarified it, he spoke in many narrations about the qualities of the leaders, the rights and responsibilities of the leaders, the importance and the necessity of the leaders, but he simply never appointed the leader.
I say appointing the leader by name is not of much importance, Rasul-Allah (saw) did what is more important and what is more needed.
A- He delivered the whole message and Allah completed the religion through him, he clarified every fundamental matter and explained the laws and the rulings, he forbade us from all that angers Allah and enjoined upon us all goodness.
B- He established a solid political foundation for the Muslim state in Madinah, although simple in its structure yet it is an entity that the Muslims can rely on when dealing with outside threats.
C- He raised and prepared a young strong generation of his companions who embraced the message and were willing to sacrifice their lives for it, they carry the knowledge of the Book and they were the ones whom Allah constantly praised in the Qur'an and he promised them victory and support over their enemies. Among them were politicians and scholars and warriors and men of piety and men of wealth and they are the best of generations.
D- He instructed his companions to listen and obey to the first man the nation agrees upon and to advise him and stick together like one solid body and he advised them to consult in their affairs.
E- He was informed by Allah about every matter that shall happen and that the religion will be aided by Allah and that there shall come a time when the name of Allah will enter every household and that the devil has lost all hope of being worshiped in this nation as he said in his farewell sermon.
We can conclude this by saying that the messenger (saw) left the matter in the hands of Allah as he believed that Allah is the truer successor and to him shall return all affairs, he (saw) had absolutely no fear for the future of this nation and Allah fulfilled his promise and the religion lives today and thrives.
We see this on the ground of reality, when the nation was able to overcome the calamity of the death of the Prophet (saw), they were then with the grace of Allah able to fill the political gap on the same day without any Fitnah, after this they were able to face the threat of the hypocrites who turned back on their heels, after this the nation began to spread the message of Islam to all nations and they succeeded in defending against the big superpowers of the Romans and the Persians, this was the reign of Abu Bakr al-Siddeeq (ra) the successor of Rasul-Allah (saw).
So what blessing do we seek after this blessing!?
Now that I am done talking about the matter of leadership and politics, comes a Shubhah or a doubt.
You seem to have quoted a narration which says: "Man Kuntu Mawlahu, Fa `Aliyun Mawlahu" Then you said that this text means that `Ali was appointed as leader after the passing of Rasul-Allah (saw).
I say, we do not understand from this text what you understand, we understand that this shows a high station for `Ali and this is a command that we must love him and be close to him, nothing more nothing less.
The key word here which you are referring to is "Mawla", I'll simply copy for you from the classical Arabic dictionaries what this word is used for.
The expert Arab linguist abu al-Hasan `Ali bin al-Hasan who was known as Kuraa`i al-Namli, this man lived in the third century and he writes in his book of language al-Muntakhab, page 404, under the title "Baab-ul-Mawla":
المولى: المالك, و المعتق, و المعتق, و الولي في الدين, و ابن العم, و الجار, و الحليف, و الصهر
[The Mawla means: The owner (of a slave), the one who frees a slave, the freed slave, the one who is close to you because you are of the same religion, the cousin, the neighbor, the ally, and the husband of your daughter.]
The renowned Arab linguist Muhammad ibn Mandhour, he writes in his book volume 15 page 405, under the section of "Wali":
الوَلْيُ : القُرْبُ ، والدُّنُوُّ
[Al-Walyu: Means the closeness and the nearness]
Then he says:
والمَوْلَى : المالِكُ ، والعَبْدُ ، والمُعْتِقُ ، والمُعْتَقُ ، والصاحِبُ ، والقريبُ كابنِ العَمِّ ونحوِه ، والجارُ ، والحَليفُ ، والابنُ ، والعَمُّ ، والنَّزيلُ ، والشَّريكُ ، وابنُ الأُخْتِ ، والوَلِيُّ ، والرَّبُّ ، والناصِرُ ، والمُنْعِمُ والمُنْعَمُ عليه ، والمُحِبُّ ، والتابعُ ، والصِّهْر
[And the Mawla: The owner (of a slave), the salve, the one who frees a slave, the freed slave, the companion, the near one such as the paternal-cousin and the like, the neighbor, the ally, the son, the paternal-uncle, the guest (in the house), the partner, the son of one's sister, the close one, the lord, the supporter, the one who blesses and the one who is blessed, the beloved, the follower, and the husband of one's daughter.]
Now this type of expression assuming you know Arabic of course, is almost never used for political leadership by the Arabs of the time, and if you wish you can read the Hadith and see how they refer to political leaders, they are referred to as: "Ameer, Imaam, Khaleefah" the most explicit of these is Ameer and the other two depend greatly on the context.
Finally, one last point you raised, when I posted the previous authentic narration from `Ali (ra), you responded by saying:
"As shias we believe that some sunnis throughout the passage of time purposely alter hadeeth and add false hadeethes as well."
I ask, how do you define what is authentic and what isn't?