Fighters who would benefit from having another trainer and underrated trainers

I believe Amir Khan would benefit from working with another trainer...havent really seen him improve as a fighter even though he has had success with Freddie Roach who is a good trainer but a bit overrated in terms of improving guys, most of the guys with him were established not works in progress or novices. ,..,Id say he would benefit from working with emmanuel steward who would improve his jab and make him sit down on his punches more other guys.....Jean Pascal all the physical tools need to work on punching technique and ring generalship jab as well , Zab Judah waited too late, Paul Williams to sew up that defense use jab more, Andre Berto defense and jab,