To be honest, the more I think about it, I have a theory that one of Mearls' roles as Team Lead is Devil's Advocate. As in, the design and development guys' job is to freely innovate and try things out. Mearls' job is to act as a voice of conservatism, of those players left behind, of the ephemeral "feel" of old editions. One of the problems of 4e, completely apart from its quality as a game, was that for a subset of players it didn't "feel" right, or it didn't easily support their style of play, or at least seemed that way on first glance. So Mearls' job is to say "Okay, is this simple enough for B/X players? Will this cause dissonance for those who've played hp as meat (despite explanations to the contrary in every edition)? Will this ability break immersion? Is it abstract enough for all to enjoy, or has it tipped into the area a significant number of fans find dissociated?" Things like that. That's essentially the only explanation I find for the Mike Mearls who once coined "Mother May I?", took the piss out of Keep on the Borderlands, and was a member of 4e's design team virtually from inception to now, would now be touting rulings not rules, core simplicity, launching the playtest with the Caves of Chaos, and now talking about shouting severed hands back on. Unless he's Born Again Old School. And basically, that dynamic was on display in the podcast.
It's just a theory, though. Not trying make excuses or persuade anyone. It could just as easily be bunnies.
Eh, Mike was never IN CHARGE of anything in 4e. I don't know why people insist on elevating his role there. He was just a worker bee among other worker bees, one who apparently came up with a fairly important piece of 4e mechanics in a one-week design huddle in the midst of a 2 year development program. It was Rob and Bill and etc who were calling the shots, not Mike, not until they were booted and he was put in charge.
Even from the start of 4e Mike has made no bones about being a 1e fan. If you go back over the things he's written since 2008 when I started paying attention that's fairly clear. His one adventure contribution to 4e, KotS, is a perfectly stock AD&D adventure in fact. Its a rather horrible 4e adventure, almost a poster-child for what is wrong with WotC adventures, but it is at least a workable 1e/2e adventure with a dungeon, a bad guy, a couple side quests, various humanoid baddies, a couple monsters here and there, and some treasure. Its 3e incarnations were better (Sunless Citadel for instance, which is a rather good adventure of that ilk) but published in say 1983 KotS would probably be remembered today as an enjoyable if not outstanding effort.
Likewise if you look at the L&L articles Mike wrote at the start of his tenure in the driver's seat at WotC you will find a love of player challenge centered sandbox exploration play, a rather old-school sort of taste. Recall his attempt at a "choose your own adventure" sort of illustration of D&D play with the survey every week asking what your adventurer would do next in the dungeon? Its a fun sort of play, but only one niche of what D&D has been about. I certainly don't know that this is ALL Mike is interested in, but when I look at his adventures, his play examples, the game he is writing now, and other statements he's made, including the podcast, it is hard to escape the notion that his ideal would be to be in Lake Geneva in 1973 sitting next to Rob Kuntz and Old Geezer delving in Castle Greyhawk.
While I think Mike is a fine guy and no doubt he has a mission of serving all D&Ders and I'm sure would be very pleased if he can do that I am no longer confident that he's got the wide perspective on play styles and etc that would make that happen. That or the constant pressure of dealing with game design plus community relations and etc has reduced him to only being able to really consider carefully a much narrower range of options. He seems to be steadily but surely cutting back the scope of his DDN efforts over time so that as things have progressed we have gone from a game intended to serve as a platform for all future play in any imagined style of D&D that is reasonable for D&D to a much more limited remodel of essentially early 80's era TSR AD&D with some additional aspects drawn from late 90's 2e and/or early vintage 3e perhaps (we have yet to see MCing and you could trace background/specialty/etc back to many different points from 2e onwards).
Of course it is possible there's is/was a more progressive game designer buried somewhere there within Mike. I dunno, never talked to the guy or played with him, but if so it hasn't been on display much in the last 5 years. That could be a change of heart or just a fondness for D&D specifically to be a certain way, but he's sure doing his damnedest to make 1983 come back. If he was just a "devil's advocate" then the resulting game design would look much more progressive IMHO.