Considering how good Herbert is in the NFL I think you can make the case that, while 12-2 is good, not properly utilizing Herbert prevented them from playing in the playoffs and potentially winning a title. But obviously that's just a wild guess.
It's okay to be critical of some of Mario's decisions with the hope that he learns from it and gets better. Others have stated this but OC is definitely the most important hire. Need Mario to really be comfortable with opening up the offense and letting TVD eat.