His first decade in charge of his setting was brilliant. He made a very specific setting with a very specific feel. That setting is still in use today, largely unaltered, having resisted many decades of mistakes that Marc made.
Some mistakes were in those he entrusted with the game (leading to such obvious and broadly-accepted mis-steps as Virus, the Black Curtain, the Empress Wave) as writers who naturally had a job and were of course not bound to in any way love the product they'd been told to write for next "exercised their creativity" and made mistake after mistake with their development of the setting. Meta-plot was the fashion and they wanted to shake things up. "How on earth do we create adventure in this setting? Let's destroy it and build anew in the chaos!"
Some mistakes were in the technical implementation of his own ideas: T4 was a shambles and T5 was intellectual onanism.
I'd suggest that few of these are even arguable: they split the fan base in ways that echo down to today, and they shrunk the market for the game in ways that Mongoose - the best custodians of the game in forty years - are even now having to work hard to try and reverse. Most of this post is just my opinion, and de gustibus non est disputandum. But the sales don't lie, and at a time when the rest of the TTRPG industry went through a gentle, albeit ultimately doomed renaissance, Traveller sank.
Some mistakes were due to his own boredom with the setting: see his approval of some of the above decisions when he was paying attention rather than focusing on - quite naturally - putting food on his table. And then there was AOtI - absolutely clearly a result of him reading Altered Carbon and thinking "I'm having that!" - which introduced changes that would wreck most Traveller campaigns if people actually thought through the consequences.
Those consequences, importantly, are something you are really the first to systematically demonstrate in a Traveller game product (maybe without even the "Traveller" qualifier), and you do so very well, I believe. By the end of Singularity a thoughtful reader can see just how complete the replacement of the 1105 Traveller in the light of those changes would really be (which, again, you explicitly state).