Defense finished 10th in Yards and 9th in points playing the 4th hardest strength of schedule behind the Falcons, Panthers and Packers. This despite the injuries at OLB that hurt our pass rush.
So the fact is that side of the ball is making progress and if Fangio stays, there is no reason to think it won't continue to do so. I have no clue who will be the better head coach but McDaniels has very little experience when it comes to the run game being the focal point of an offense. He has spent most of his career in New England where the run game is an afterthought. Something you do to give Brady a breather. They have run quite well recently but a lot of that is because of the fear of Brady.
While Nagy hasn't called plays, he at least has experience in an offense that features the run games. An offense that is more balanced in the sense that teams weren't geared up to stop Smith like they were Brady. Given our strength right now is at RB, I am not sure why you think Nagy is just a QB whisperer when Kareem Hunt experienced his most activity during the time Nagy was calling plays. If anything, it is Daniels who has very limited track record being committed to anything other than the passing game.