Khan went from a devasting loss to Prescott to a title holder under Roach which was a huge achievement. Manny has achieved huge things while he was with Roach. OK he lost to Marquez but you are not going to win them all and father time will always get you in the end.
Both Marquez and Danny Garcia are both formidable opponents and them winning has more to do with their performances than Roach's limitations. It seems with Khan that Roach worked on his strengths and his deficiencies were never addressed. Changing habits is tough and takes a huge amount of time to become natural. It is risky and Khan may well have been vulnerable in that transition and notched up loses earlier.
I think it will be a long time before we will see any real changes in Amir Khan as he has strongly ingrained habits and the changes will take a very long time to become second nature. It is one thing attempting to make changes and another for them to become second nature. He has had a good run with Roach ,personally I think we have seen the high water mark in his career and he has reached his level. I see him doing very well but coming up short in the really big fights but you have to give him credit for getting out of his comfort zone and trying to rebuild himself.