If you look at Perry's track record no coach in his right mind would have given Perry another start. It was reported last offseason that he wasn't putting in the work and trying to learn a very very simple offense. Then he he put up videos of himself flashing stacks of cash , then this offseason he posted videos of himself boning chicks. You might notice a pattern of behavior. Rosier had his limitations, but he also won 10 games the season before. He also ran Richts offense the way Richt called it.
There is no coach in D1 that would swap out a QB who had totally earned the HC's trust (and won 10 games) with an unproven, demonstrably immature qb who, when given his opportunity to step up, promptly decided to ignore the HC and call his own plays (not unless the kid has Cam Newton-like talent and can carry the team to a championship on his own). Perry might be good, but he isn't anywhere near that talent level. Maybe if Perry had lit up UVA with his own playcalling, Richt could have seen his potential. Instead Perry threw pick after pick.
Sorry, bro, there are lots of reasons to dump on Richt, but benching Perry indefinitely for not showing that he was ready to lead the team is not one of them.
Should he have started Williams? Yes. At some point. I think once Miami was out of the running for the coastal, Richt should have taken the opportunity to evaluate Williams. Perry was in his doghouse and wasn't going to get more burn. Williams, as far as I know, wasn't as much of a problem. I would have liked to have seen Williams with 2 or 3 starts at the end of the season.