That had more to do with JJM needing more reps in practice and he didn't get those because it was a Thursday night game. Hence why he played the next week against the Lions and had a surprisingly decent game.
Eh, I think a lot of those rumors have been astro-turfed to retroactively salvage KOC's reputation (hence why they all came out after Kwesi was fired, piling on the scapegoat). He definitely wanted Jones to sign here and compete with JJM and did not want Howell as QB2, but otherwise I believe he thought he could coach JJM up. And then it became apparent once he started playing against NFL speed that he wasn't ready, and KOC wasn't prepared for that.
His mechanics were not a problem at Michigan nor were they in training camp - he reportedly had a really rough minicamp in 2024 and rebounded in training camp to the point where it seemed like he could push Darnold for the job. And even in 2025 training camp he had a fantastic joint practice against the Patriots where he looked a lot better than Drake Maye. It wasn't until the real games started and then the injuries worsened the issue.
I'm seeing people claim that KOC never wanted to draft JJM, which is absurd and plain old gaslighting. JJM was a great fit for KOC's offense, being one of the best intermediate passers in college football who played in a pro style offense which would supposedly speed up the transition from college to pros. And zero injury history, to boot. But the light bulb doesn't turn on for some prospects...
Not sure I believe he was "forced to", he was probably chomping at the bit to get back into the lineup to get more reps.
Overall I agree that maturity (along with the injuries, obviously) was the primary issue.