I think to me, the general concept of the religion is proven by logic. And the logic of the religion is only emphasized in the holy book of Islam or offshoots of Islam. Then you just have to see if the offshoots of the religion can be true or not. I see that they aren't true.
The general argument mainly is in God's Majestic Praise in how he uses exalted servants and brings up their station through choosing them for his religion, and honors their followers and favors the believers with an extreme grace with them through their trial.
The affair of divinely chosen families, consisting of exalted chosen servants that succeed one another and are tied in one cause, has a majestic praise linked to God. That is why the Angels tell Sarah they should not at all be wondering and surprised at God giving them Isaac in old age, and after Isaac, Jacob. The reason being is that this is "the affair of God" and that God is "Praiseworthy, Majestic". They being an exalted chosen family who God's entire blessings of creation and his entire mercy on creation is upon, should not wonder at this, because this is God's way with his chosen ones and humanity.
In the same way, it makes sense that a revelation is available in these times, and that God appoints a group of chosen people to guide the nation.
I also believe that goodness, beauty, and honor, have unseen reality, and that revelation and code of the religion has an inward reality, and that God in his wisdom has shown a majestic praise with regards to appointing of the best of humans as Guides in the spiritual journey.
Ibrahim was already a leader appointed by God while a Prophet and a Messenger, and an example already to people, but what was meant by him becoming an Imam was that he was becoming the Guide in the spiritual journey in all stages to those who tread the guidance of God, and this station was attained by the Guides after they were given vision of certainty and were found to be patient. Ibrahim attained this after having offspring, while he was given offspring after his Prophethood and Messengerhood, according to Quran.
As I believe there are unseen forces of evil and they have spiritual powers to misguide humanity, I believe there is a more exalted spiritual power that manifests as a miracle and beyond that of the fake powers in guidance of God, like the Staff of Moses proved the sorcery to be but sorcery while his power to be from God.
I don't see any book claiming to be a revelation emphasizing the guidance in the unseen journey by a divine guide that is a light, a way, a companion to the journey, other then the Quran.
The wisdom of choosing ALIVE people to be these guides also has a wisdom, as that keeps us connected to the living best people of our time, and always makes us incline to the best person alive on earth who shares with us the grief, the hopes, and the observation of the events of our times, and is a witness upon the people, in which every people will be called with a witness from them.
The inheritance of the light/guidance and the remainder of God on earth inheriting from chosen ones before him, has a an exalted wisdom in the Quran.
As God is spiritual and hidden, there is hidden unseen stages, and there in an inward spirit to the outward connection (salah) in the inward world, and these stages of the inward journey is best manifested by way of example, of showing the way to tread.
The Divine light of the Names of God is most manifested through the glorification of God through their spiritual light and inward knowledge of God.
To imitate glorification of God they show through out the stages, praise of his beauty and majesty, is of the unseen affairs, which I believe is the delight of the eyes of the mystics.
We been created for something higher, to tread upon spiritual path.
I also believe that these exalted servants, just remembering them, proves the existence of God, as goodness honor and morality of theirs which we can remember is linked to the existence of God and his Worship and sincerity to him, showing that morality, greatness, and beauty, encompasses worship of God and this worship of God can only be exalted and moral if God is true.
Attachment to them is attachment to Worshiping God in sincerity, and is a straight path.
The wisdom of exalted families and tying their cause together, I find emphasized in no holy book but the Quran. I see eternal wisdom in that, and appreciating the message of the last Messenger has been said to be nothing but the love of the last of such families (42:23) and said to be a path to God (25:57).
I believe the wisdom of the Mahdi, the emphasis on the divine rule of Dawood and Sulaiman, the wisdom of Talut being appointed king, has a more universal need of God's rule to humanity, and God has linked needing his chosen ones with needing God, and the Mahdi being the one who is promised to rule the world with the divine rule of God and his revelation and his wisdom, bringing justice to the world, I believe is of a majestic praise.
He being from a divinely chosen family and being tied to their cause is also of a majestic wisdom, emphasized by the Prophet "The Mahdi is from us, Ahlelbayt".
I believe this affair is tied to God and his Majestic Praiseworthy Names.
When the world wants to come to God and wants the rule of Mohammad the last Prophet, they will come to his final successor and God's representative and ruler on earth.
At the same time, people go to extremes with his chosen ones, and that's why there is wisdom that Quran emphasized you have no intercessor or helper besides God, and emphasized on praying to God alone and not worshiping others or taking the chosen ones as Lords.
The balance. This to me is Islam. It's the balanced path, in which we don't equate or belittle God with chosen ones, neither do we neglect the rights of his chosen ones and their noble station, by which God has made them the means of approach towards him.
And it emphasizes the intercession and intervention of his Angels and chosen ones, do take place by his permission, so to pray God for such help and guidance and mercy, and God will surely aide us with his his unseen forces over the dark forces.