[However when it comes to "Imammate", the Quran shows every human will be called with their "Imam". It also says that with regard to a witness from them.]
What's your objection to us saying the Imam (example/leader) is the Prophet (saw) OR the Qur'an? Isn't that what `Ali taught us? That the Qur'an is our Imam?
Very true. That's what we Sunnis believe in. From both the Quran and sunnah, all sorts of branches of rich Islamic diciplines are derived and that will continue until yaum Al-qiyamah. Only a deluded person going to deny that fact.
Indeed, true is Allah's words when He said:
1) In Surah Al-Isra' ayah 9:
إِنَّ هَٰذَا الْقُرْآنَ يَهْدِي لِلَّتِي هِيَ أَقْوَمُ وَيُبَشِّرُ الْمُؤْمِنِينَ الَّذِينَ يَعْمَلُونَ الصَّالِحَاتِ أَنَّ لَهُمْ أَجْرًا كَبِيرًا
Indeed, this Qur'an guides to that which is most suitable and gives good tidings to the believers who do righteous deeds that they will have a great reward.
2) In Surah Al-Ahzab ayah 21:
لَقَدْ كَانَ لَكُمْ فِي رَسُولِ اللَّهِ أُسْوَةٌ حَسَنَةٌ لِمَنْ كَانَ يَرْجُو اللَّهَ وَالْيَوْمَ الْآخِرَ وَذَكَرَ اللَّهَ كَثِيرًا
There has certainly been for you in the Messenger of Allah an excellent pattern for anyone whose hope is in Allah and the Last Day and [who] remembers Allah often.
Compared that to the so called hiddened "true" leader claimed by Link. What example or guidance the so-called hiddened "true" leader has shown his followers to live their lives as true muslims?
The matter of fact, whatever laws they derive are coming from their dead imams (mainly Al-Baqir and As-Sadiq) and not that hiddened "true" leader or "imam of this age".
Actions are a state of being. Words are words. The right "honesty" and "patience" is a state, actions themselves are a state, the Imams of guidance they been revealed good acts, God shows them the states, both for them to follow and to show their followers.
You are right as far outward words go, Imam Mahdi is not what we use for that. We use the Twelve Captains of the past associated with him, the Messenger of God down to the 11th Imam, as well his pure mother Fatima.
Satan uses his minions for outward words, and misguides through them, but the main misguidance is not from the words of men under his control, but from states that he inspires people to follow through his army of hidden beings (Jinn) that watch us.
The fact is we have many watchers that see us, but they don't truly see us, because they themselves are blind.
We need to combat the eyes of Iblis army with that of vision from true eyes. The Quran shows we will be called with a witness from ourselves.
It also states every people will be called with their Leader. The sense of "Messenger" type leadership, Bani-Israel had 13 of those, starting with Moses and then 12 Captains who succeeded him. Many verses show that he was followed up by Messengers, we can conclude even Talut eventually became a Messenger.
But they had one Captain for the ship that sails by the name of God during their time in the sense, that he would lead them on their inward journey.
In the sense of "Ulil-Amr" (those who possess the authority), Imam Ali remains that, so does Al-Hassan, so does Al-Hussain, and you are right, we take guidance regarding "referring to God and the Messenger" through the Ulil-Amr.
But as far as referring to "the Nabi", then Nubuwa has higher knowledge not always conveyed in Resalah, although we get a scent of it through Resalah and it's conveyed to us. The Quran connects to the highest possible states, but to hear the Quran in that state, we must hear with the ears of the Guide of our time.
Just as Satan can make us see and hear according to falsehood, the Guide of our time can help us and aide us by lending light/water/rain and being with us in ways we do not understand.
You believe the envious eye of mere low creatures can have effect on a soul and afflict him with negative influence, I don't see why you don't believe the witness can help us with his vision and guide us, and influence us positively.
While it makes sense there is many falsehoods and paths to falsehood making a need of many Shayateen, when it comes to the path to travel to God and what we must do, and wisdom, it makes sense the chosen ones who inherit the book and race ahead all in good deeds from the servants of God are those entrusted to make us see and manifest the wonders of unseen beauty and majesty.
Indeed all past Guides can help our sword of honor and vest us with spiritual help, as they do time to time, but the one who is perpetually the leader and guide and witness over us, is the one who the Quran says "the day every people will be with their Imam", and "when every people will be called with a witness from themselves".
May God increase us in guidance and faith in the unseen.