I'm reserving judgment on Rattler. Yeah, he "lost his job" at OU, but there was a lot going on there that wasn't his fault. Even some OU folks have conceded that Riley wasn't coaching him well, speculating that he already had his eye on the exit, given how quickly he departed for SoCal. Not to mention, they were 5-0 when Rattler was demoted. To that point, he had a 75% completion percentage, 11 TDs and 1500 yards. He was on pace for about 3600 yards and 27 TDs. He wasn't exactly playing poorly. Fans were just agitated b/c they weren't obliterating teams and it was the classic "the most popular man on campus is the backup QB." Williams was highly touted and fans just got antsy to see him and the thing snowballed.
I don't know how good Rattler will/won't be BUT he is unquestionably an upgrade over last year's QB situation.