I don't know if I would put that down to Roach, Khan made the same mistakes against Peterson and failed to realize why that was a close fight. He needed to say "Coach we need to change some stuff up maybe add some elements do you have any ideas?" if he didn't say that or anything similar that is the fault of Khan.
That said Roach is a simple trainer, hell just watch Roach as a fighter it is not like he was some great tactician in the ring. There is something to be said for the KISS method in that ring but if one goes that route the guys needs to not make crucial mistakes which Khan has made for a long time.
I liked Khan as a fighter for a while because I figured he would have some growth or at the very least cover some flaws, I guess Roach can shoulder some blame but really was Khan going to really listen to any trainer and take what they had to say to heart.