No doubt. You def need good players. I think we all agree there. And yes, the question is just how much of an impact can and does a coach make. It's completely subjective, depending on who you ask.This is the whole debate -- how much is it the coach?, how much is it the players? No matter how "good' the coach is I think they need some talent at their disposal for success.
Good players always make the coaches look better, fair or unfair.
Personally, I look at John vs Jim and I just have a hard time believing John wins as many games in SF as Jim as over the last year. Now, maybe that is just a thing where Jim is the perfect guy for SF, and more specifically Alex Smith. I mean I do think certain coaches fit better in certain organizations with certain players.
Again very subjective. It really depends on what angle you chose to view things. What you value in coaches,etc. I do not believe John has gotten the most out of team the last 4 years but overall he's certainly had a positive impact. Grading him I'd give him a B or B+.