Is Islam's traditional historical account of the origins and first couple of decades of "Islam" reliable by modern standards?

Can we assume that some broad/concrete claims like these are true?: that a man who is the historical basis of Muhammad actually lived between 570s - 630s, he was born in a polytheistic trade metropolis called Mecca ruled by a coalition of tribal patriarchs, and at some point he led a political opposition and gained social support, and they had to migrate to Yathrib where they established a "commonwealth" that eventually absorbed the entire peninsula, this state somewhat resembled a prototypical republic with meritocratic elements and also constitutional concepts that echoed Magna Carta (some sort of election, accountability, and impeachment mechanics are implied and equality of the ruler and the ruled is emphasized in Muhammad's successors' inauguration speeches (Abu Bakr and Umar), Muhammad didn't establish his own dynasty (though Shia disagrees), there's the Medina Charter that appears to function as a social contract between different religious communities constituting a single ummah (polity)), then there is civil wars and transition to a monarchical empire by the Umayyads and in the course of these events significant figures were eliminated who were Muhammad's contemporaries, close circle, and direct descendants.)

Can we be confident that this picture approximately represents what actually happened? If yes, what else can we be sure about? Are the details as certain as the overall picture?

What do we know about the origins, developmental stages, and spread of "Islam" as an idiosyncratic ethno-religious identity, that eventually began to claim superiority to/discriminate against other surrounding identities? What do (or can) we know as an unsuspected fact about the "original movement" that started in Meccah and migrated to Yathrib, their beliefs and world view? Did they believe in monotheism? If so, were they initially a Christian or Jewish sect or under their influence? Or were they independent in origins? Did they believe a man among them had spiritual experiences and divine inspirations? Did they have this guru figure like Paul, a scholar-king/rabbi-warrior walking among them? Did Muhammad exercise such privilege and authority? Does this image contradict the depicted political atmosphere of Medina? Can the first Quran manuscripts be traced back to Muhammad's lifetime? Is there an alternative, well grounded theory of when/how/by whom the Quran was produced and codified? Is there a possibility that Muhammad did not claim prophethood or preach the Quran, and that these are later constructs by future generations who anachronically ascribed them to him and a mythical past, suiting the needs and conceptions of their time? (If I wanted to ascribe divinity to a scripture I wrote, I would rather say some widely respected historical figure originally preached it instead of saying I received it. As long as I convince people that the book is holy, I don't have to be the prophet myself, it's better to exploit someone's name who's already influential -and dead- than use my own status. I mean, Paul didn't say he was Christ--he said he represented him, which was much easier.)

In other words, did Muhammad and his contemporaries found Islam, or Muslims? (like, was it Jesus or Paul who founded Christianity). Could it be that "the Prophet and his companions" are figures legendified/mythologized by Muslim societies, scholars, and rulers, if not completely imagined by them? that the "Muslim ummah" becoming a distinct theo-political entity was actually a later development, that anachronically traced its origins back to 610s? Maybe they needed an origin story for this new ethno-religious "supertribe" they created (similar to modern nationalism), so they came up with a charismatic founding father, a divinely supported war chief, and built up sacreds/creed to mark their irreconcilable difference from rival tribes, much like the pre-Islamic Arabs would do?

This is more of a hypothesis/speculation than a question, and I don't expect a definitive answer, but I don't like conspiracism and I request a historian's guidance to set me on a scientific, methodological approach to such questions, to test these hypotheses. I recently heard about Dan Gibson's Petra theory (he claims the real Meccah was in modern Jordan) and I realize his methods are not exactly scholarly, but he makes some undeniably good points on the resemblance of the geographical descriptions of Meccah in the Sirat with real life Petra and I don't know what to make of it. If such a thing is true, what else can be a complete fiction about Islam? I don't like extreme positions like "Jesus is Christianity's forgery, Buddha is made up by Buddhists", I don't believe you can bring such influential historical figures into existence out of mere imagination, but there seems to be an Orwellian 1984 situation going on with Islam's history. (A lot of civil wars and revolutions, the "Prophet"s grandchildren getting killed by Muslims themselves, bloodshed in their own "Holy City"... is it wrong to assume politics must have played a huge role in writing/censoring/forging history?) Now I'm in this skeptical position that there is zero certainty beyond the fact that there has to be some kind of historical basis to these characters and events but that's it.