Meh. If he's going to post something so incredibly stupid from a developer perspective then I think the dig at his credentials is fair play, he should know better as a "developer" not to post such a dumb ass take. Maybe the dude is just washed up since he hasn't done anything important since World of Warcraft and that is literally the only thing anyone brings up when they talk about him, something he did 20 years ago.
Considering how much of an asshole he is on Twitter, I have my doubts he left Blizzard based on moral grounds.
Looking at what he did more recently, founded an indie studio and then literally got booted out of it because he squandered all of their money on a bus instead of spending it on the development of Firefall, he was also hated by his own employees: Ex-Red 5 Staffers Blast Mark Kern's 'Destructive' Behavior
I've a feeling that Mark Kern is one of those "team leaders" who found success thanks to the great team beneath him, not thanks to his leadership, his biggest credit is "Team Lead" and by all accounts he seems like a bit of a shit leader, even more so I think if he was so brilliant then he would have found employment elsewhere but now he spends his days as a Twitter troll, not a developer.