I heard one of the announcers commenting that the OSU running game started improving immediately once OSU settled on Bowman as the QB because he is the least mobile of the 3.

Accordingly, OSU had to drop most of the zone/read stuff from the playbook, which made it much easier on the OLine because it removed the guess work on how they might have to block (mid-play), and allowed OSU to put the TE in motion or send the FB into the hole in advance because they now knew what play was actually going to be run (e.g., run/pass)

I don't know enough about blocking assignments on zone/read plays, does that analysis make sense (that the blocking assignments were more predictable)?

The changes in offense pass blocking (few sacks) and rushing (Ollie going wild), sure seem to coincide.