Except Crosby has always been right around 200 lbs. Pretty big difference, esp. with most of that being lower body strength allowing for loads of puck protection.
IINM McMichael did say he put on some more muscle in the off-season and he does train with Gary Roberts & Co. But there's training and there's training. There's doing it and there's living it. I don't know that he's got that dawg in him, essentially. And so what's the carrying strength? Initially it was a certain offensive craftiness but that seems to have waned along with his confidence to some degree. As-is it doesn't seem that far off for him to fall into the rut that's claimed other finesse players under Lavi who've not managed to dig their way out of it.
If he produces he can write his ticket to wherever he wants to play but that requires a lot of determination and ability to translate emotion into results. Thus far he's been sort of a bottom-feeder offensively and needs to find more ways to impact the game overall. The underlying stats may be strong but there's still a lot lacking to endear himself to the coaching staff. As much as maybe those things are superficial or wrongly prioritized they are fairly simple and easily managed areas. If physical immaturity is less of an excuse it primarily points to mentality and I suspect all along that's been the larger issue. These days if players really want to play interior they'll have trained like it for years and years and not just at the age of 19 or 20 when it becomes absolutely essential.
He's reported to be at 185/190 this season, and as you pointed out he's training with Gary Roberts. Or you could look at any of the names I dropped in the subsequent post for other players who don't have stand-out heights or weights or overwhelmingly fast straight-ahead skating, yet have been successes in the NHL. You're seeing the intentionally hyperbolic name I chose (Crosby) and losing the forest for the trees here. There's nothing in his physical attributes preventing CMM from having similar success to, say, Mikael Granlund (5'10" 180-185lbs, been described as an "average" skater) or Joe Pavelski (5'11" 190-195lbs, was never an imposing player or a burner, and his current forecaster scouting report states "He is not big, fast or physical--just effective.").
Gary Roberts isn't exactly known for letting his trainees be uncommitted. The fact that you (and others) are now trying to bring up commitment and work ethic as question marks for CMM is some real post-hoc justifications for the coaching staff burying CMM. You're searching for some reason why he "hasn't endeared himself" to the coaching staff, to the point where there's now questions being drawn in areas where questions were never drawn about this player previously.
"If the coaching staff doesn't trust him, there must obviously be something wrong with him, right?" I understand the search for rationale there, but I don't agree with leaping to a conclusion regarding it. Moreover, this head coach has shown this to be a pattern with him. He holds young skill players to a different standard than other players, especially when compared to veterans. CMM wasn't the only player in Lavi's doghouse last year, and he's not the first example of this happening. Lavi set Kevin Fiala's development back years in Nashville, and it's not surprising he blossomed as soon as he got to Minnesota. After the Richards/Carter trades in Philadelphia, the Flyers foisted a young team upon him, and Lavi still had Matt Read skating more minutes than Voracek or Wayne Simmonds. He had Brayden Schenn bouncing in-and-out of the line-up in Philadelphia, and then Schenn posted 41 points immediately after Lavi was fired.
Occam's Razor points towards Laviolette here, not any commitment issues from CMM.