I think a couple of things need to be said about Cavill's shape and Affleck's shape because there is still a bunch of misconceptions around here. Yes, they did not do make up or touch-ups on Cavill's abs but they did do some things to optimize the presentation of his physique in his shirtless scenes. On both the oil rig and when he steals the clothes, Cavill is wet, which gives him a nice sheen and helps show off his definition. Also, both scenes are lit relatively softly. Soft lighting is good. Harsh lighting washes out definition. So they didn't cheat, but they did help.
As has been mentioned, Afflect looks far from phenomenal, even in recent photos, which has nothing to do with his drive or commitment to the role. As has been mentioned, his Gone Girl commitments and Fincher's production overruns have interferred with Affleck's preparation time. He was told to stop working out because he needed to look like an average, middle-aged guy for Gone Girl.
People also need to be a lot more realistic about what can be accomplished naturally in just a few months. It doesn't matter if you have a personal chef or killer personal trainer, the human body puts on muscle mass relatively slowly. The result is that Afflect looks like a reasonably fit, middle-aged man right now. Thus, his current physique is really quite different from what the Batsuit shows. The suit is helping him out a lot as a result. It is highly unlikely that he will continue to grow as the shoot progresses given the time commmitments and the difficulties keeping up with proper sleep, diet, and exercise during a big budget Hollywood production. Unless Ben intends to "ride a bicycle", don't expect miracles.