Chan did fine while he was here.
I'm going to say the biggest issue with Roman was calling the game for a developing qb. As with Kap, he seemed to want the qb to make a leap from a running qb to a qb he wasn't (pocket passer) too quickly and didn't adjust his play calling when it didn't work. The season is short, the time to work on the passing game is when you have the game in hand not when it is undecided.