Herbert is bad when pressured. He went 12-2. This indicates that he's rarely pressured and that Oregon indeed has a distinct talent advantage over the other teams that they play.
Herbert is a front-running QB who isn't relied upon to win games for his team. Mahomes was that dude in college, but still lost because his defense was atrocious (5th best offense, dead last defense). I mean, Mahomes threw for 5,052 yards while Herbert was sitting at 3,471. That's a BIG volume difference and it's not like Herbert is a running threat. The guy averages 140 rushing yards per season.
It's not like Mahomes transformed when he got the NFL just like Herbert isn't going to transform. If you have a QB who can't overcome deficiencies and who can't play well in spite of them then he's precisely a Tannehill.
Don't ever compare them again, honestly.