I normally agree with most things you have to say on here, but with this, I completely disagree.
If McDavid had truly checked out, meaning he hit his "f**k it" point, then his demeanor would be consistent through all situations, and it isn't.
When someone has mentally checked out of a given situation apathy tends to set in and their reactions to the negative will mirror their reactions to the positive, in this case wins and losses. McDavid still is celebrating the wins like he always has, and still gets pissy over the losses, that indicates someone who still gives a shit.
Now that doesn't mean he can't be frustrated with how this organization has been run during his time here, which he should be, it's been a mess, but he's too competitive and too driven of a person to become apathetic about wins and losses to the point it would effect his performance on the ice. He didn't become the best in the world on talent alone, his drive, focus, determination, discipline and work ethic are completely off the charts to be where he is at in his career. I find it almost impossible to believe that he would become apathetic towards wins and losses, and would just all of a sudden start mailing it in, that's not in his DNA.
I do believe he has some sort of nagging injury that isn't serious enough for him to miss time, but is just serious enough to slightly affect his performance.