Meh... he isn't striking out much, his Babip's low so there's regression there, xWoba far better than his line, and it's only been 11 games. He'll still get to his 5-6% walk rate, kid can rake, I'm not worried.
That's an interesting correlation with the changeup and injury, but I think his command is the issue, prior to last August he had pinpoint command and continually worked ahead of batters, since then not so much. And he's been absolutely pounded, maybe he was a Spider Tack guy simply for better grip?