I think Craig has 'developed' this as part of his Bond's story pretty well.
In CR he's straight out of the Special Forces, so the bulky muscles are plausible (if the the exposure they get on tv these days is to be believed).
In QoS the bulk was gone. It was a lean, ripped physique. Perhaps a little too ripped for someone who works a great deal, but the transition from blunt instrument towards a more nuanced agent was evident in his physique as well as his performance. I'm willing to suspend disbelief in terms of how Bond managed to change his physique between movies where no significant time has elapsed
In SF he's looking older (obviously) but he's allowed his physique to show it; there's the suggestion of a belly at times and the whole first act is about him being out of shape.
In Spectre there's no enfaces upon physique. He's in good shape, but doesn't look like a bulky gym-bunny.
I think Craig's had a plan from the start and followed through with it very well.
But because i don't want to see another 'Bond Begins' reboot i don't see a need for Bond 7 to bulk up for the role. Lean, fit, wiry and fast is how Fleming's Bond is and i always prefer Fleming.
Adrian Brody's physique is a little to thin for the role, but i liked what he did with his character in Predators. Against the expectations created by Arnie in the original, Brody accentuated the benefits of his lean, wiry physique: speed. And it played out very well in the action - completely believable that he out classed his more bulky rivals.
Fassbender's characters in Haywire and X-men: First Class is pretty much Fleming's Bond.