The arguments for Tawheed are more philosophical in nature and even transcend normal reasoning, and appeals to higher reasoning, and you will see Atheists always say this is ambiguous, "it's a philosophy I don't understand", so this intellectually laziness is something not to be proud of. And the philosophy of following those who God appointed as Leaders while those with no proof from God claiming leadership and authority should not be followed, is not very complicated, and is even less profound and less deep then the issue of Tawheed and how we are connected to God and his knowledge.
But it's been my experience people who don't reflect don't even understand how Quran proves Tawheed or God.
But it's worth noting that Islam wasn't revealed to scientists, philosophers or 'intellectuals'. It was revealed to a relatively simple people who nonetheless believed in Tawheed in whatever capacity they could - and in many cases those people understood it much better than you and I. But any belief can describe itself as deeply philosophical and needing higher reasoning and man will believe it to be true. I've heard some fairly ridiculous explanations the concept of Trinity - those who believe in it use their 'true' interpretations of the OT and NW to justify it, but I think I would be right in saying that for most people, it's mumbo jumbo to say the least.
If you study verses about the issue of Tawheed, they are very deep. For example the name Al-Hayu is a deep concept in itself. The issue of "Allah's Name" or "all-beautiful Names" is a deep issue.
These were explained in the time of the Prophet as the verses were revealed. Today, we are use to simple commentary, but we don't know the commentary people received from Imam Ali for example during the time of the Nabi who was the door to the city of knowledge.
There is deep teachings in Quran, and it was taught in deep manner I believe. It says it's revealed for a people who reflect.
This is not to say it's meant for elite of society or anything like that, but it's not meant to be just believed without deep reflection.
The concept that there is a being such that no being can be with him in his highness, that nothing can be with him is his absolute existence, is not such an easy concept to grasp. How do we know this? Why do we know this? How can it be possible? How did we witness this fast in the first place when Allah said "am I not your Lord".
Then comes the degree of sincerity and value we ought to give that being, and the path that treads in gaining his knowledge through that which is connected to him.
The Quran talks about "they desire his face", the face of God is a deep concept in itself. It's no easy thing to grasp. We get a general scent of it, but it's deep issue.
The Quran talks about how Allah is the light of the heavens and the earth, but how?
All this was slowly taught to the people in stages. The knowledge of the self was taught till the people saw the signs of God in themselves and in the horizons and they knew God was the truth then.
It was not an easy matter. And people were objecting, why send an Angel to you, and then you talk to us, why not just send Angels to us, or why not send an Angel with you.
They had all these "intellectual" objections as well. They knew it all made sense, the miracles were there, everything pointed to the truth, but they stoke to intellectual slogans that kept them from belief.
They are right if God wanted everyone to follow the Prophet absolutely in an absolute way, he could of sent them Angels and made the matter beyond clear, and he could of did miracles which they would not have denied or called sorcery, but this God's test.
And at the end people can be obstinate, or they can listen with their hearts.
This issue is very simple to me. God's guides to the truth and hence I shouldn't follow people who claim authority but rather those who guide by God's authority and command.
When they are not among us, I don't follow men claiming their authority or leadership.