I think it's clear GGG's time with Abel 'Super Mario' Sanchez is up. Sanchez had a poor game plan for both bouts, things like no body shots and lots more problems. Even after the bout Sanchez was saying that GGG didn't follow the gameplan and that the judges were correct, not a good look at all for GGG. So who should GGG change trainer to? Maybe Freddie Roach again who he did start out with in the wild card gym.
Sanchez is a very limited trainer strategy wise. Kept on going on about how GGG needed to keep his punches lower.
GGG and Sanchez are good, but I think a little mix-up could help, and not because Abel is not world class, but because a couple of new looks and tricks can bring some unknown and unpredictability to a 3rd fight. Prime Nazim Richardson handled aging fighters well, but perhaps a Russian speaking one could get info thru much more clearly. I'd also drop high altitude training and introduce some more scientific method, VO2Max, EPOC, modern diet and recovery, tennis does it quite well.
Abel is an excellent coach and helped get GGG to the point of being a long reigning unified champ. Abel polished GGG up alot once him and GGG started working together. It isn't Abel's fault GGG didn't follow instructions in the second fight. GGG getting a new coach at this point wouldn't make sense. If GGG is too old to carryout Abel's instructions he should retire.