FSU and Miami were pretty bad, Purdue had their day in the sun. OU didn't really miss Mayfield much. UGA ended up playing 3 currently ranked teams, losing to one.
Exhibit A on returning starters being absurdly overrated: look no further than QB at Oklahoma:
2012 - Landry Jones throws 1,000 times for tons of yards and TDs
"That's okay, the Bell-dozer will be our Tebow"
2013 - Bell isn't the thrower Jones was, doesn't even run much, nary a rushing TD
"Yeah, but that Knight kid really took it to Bama"
2014 - Knight is very average, almost as many INT as TD, OU loses 5 games
"Crap, man, Knight stinks"
2015 - Knight supplanted by Mayfield, who plays great.
2016 - Mayfield sets new single-season QB rating record
2017 - Mayfield breaks his own singe-season rating record
"Aww damn, Mayfield is gone, what now?"
2018 - Kyler Murray comes in, has a better rating than Mayfield AND runs for 900 yds, 11 TD
So maybe not specifically 'returning starters,' but more 'it's hard to prognosticate the future with any accuracy.'
Uncertainty at a position group doesn't mean it'll be a weakness. A guy who flashes greatness won't necessarily be great when he's THE guy.
