I don't think he would have lasted the entire season as a starter even before he was "tired," but that probably sped up his demise by a good amount.
Richardson wasn't ever going to be an NFL QB. He barely played in college and executives got duped by the "i can fix him" fallacy because the Bills managed to actually turn one of those types of prospects into a stud.
Josh Allen started 6 games in JuCo. And 26 at Wyoming. Style of offense more pro than read option there.
The 1 year starters in recent drafts:
Richardson 13 college starts.
Trubisky 13 college starts.
Haskins 14 college starts.
Lance 17 college starts, and attempted 318 passes. That is less than 20 per game.
Mac Jones 17 college starts
Sanchez 16 college starts
Murray 17 college starts
Not a great list of success having under 20 college starts. Bottom 2 guys are the most successful. Sanchez was protected early in his career, but when more was expected out of him he couldn't deliver.