We don't know. From a modern, historical, scholarly standpoint, we know very little about the Prophet's life. For the most part, all the sources we have about the prophet are either from the Koran, from Muslim bios written about 200 years after he lived, or Greek/Syriac sources that were written when he was alive, but that treat him like a barely important footnote.

The Koran is problematic, because it's not really about the Prophet's life or actions, it was about deeper things like the the lives of earlier prophets, the nature of god, and the afterlife. Unlike the Jesus in the Bible, there is strikingly little info about Mohamed in the Koran.

For this reason, starting in the late 800s/early 900s, Muslim scholars began collecting officially recognized biographies about the Prophet's life, which are now known as Hadith. Initially western scholars considered these largely credible, but that is changing.

Since very few people in the Arab peninsula were literate when the Prophet was alive, these medieval Muslim scholars (living well after all contemporaries of the prophet were all dead) would have had a hard time figuring anything credible by modern, scholarly historical standards.

These medieval Muslims also would have also been under extreme pressure to A) not make the Prophet look sinful or hypocritical, B) not make common practices of the Abbasid elite look counter to Mohamad's teachings and C) to give the impression that they had exhaustive knowledge about the Prophet's life, even when they did not.

As a result, the medieval biographies of the Prophet/Hadiths are not particularly credible by historical standards. Undoubtedly, there is a lot of truth there (I personally think they are largely historical) but we can't say for sure what is true and what is not. Regardless of their veracity, they tell us much more about Abbasid era (750-1258 AD) than the time of the prophet (570-632 AD).

Finally, we have what Eastern Romans and other literate, contemporary neighbors of Mohamed wrote about him. This is great, interesting research, but it's frustrating. The Eastern Romans, whether they were writing in Greek or Syriac didn't really care about the Muslims until they invaded Palestine (which almost certainly happened after the Prophet's death). These sources refer to a great teacher, or king who united the Arabs of the Hijaz, but don't really seem that interested in this movement initially. Later (during the initial invasion of Palestine) Roman sources mention that the Arab invaders are effective, and LOVE this Mohamed guy, but don't give us much details other than that. One Roman source has the Prophet Mohamad leading the the invasion into Palestine, even though he was probably already dead at that point, so it should all be taken with a grain of salt.

Any western scholar making definite, specific claims about the social structure of Mecca, the initial character of Muhammad's movement, or even the nature of Islam's raise in the Hijaz is (at best) engaging in educated speculation.

W. Montgomery Watt was writing in the '50s before westerners were skeptical of the medieval sources. He was also (commendably) trying to counter the false, racist, orientalist view that Mohammed was some desert madman, probably inspired by the devil, who started a worthless, harmful, nonsense religion. Watt was a good scholar, but things have moved on since then, and while it's possible Mohamad did have a proto-socialist, social justicey message, we really can't know.

If you want modern sources check out Fred Donner from University of Chicago. He wrote "Muhammad and the Believers. At the Origins of Islam" which is great. He also has great youtube content. Check it out: https://www.youtube.com/watch?v=QTg-uGajlak&t=238s