Honestly I think this game might address my group's biggest issue with PbtA, ( the feeling it lacked mechanical omph in play) our first game is Saturday so we'll see.
That was certainly how it felt to us having played it - a lot of PtbA games have mechanical elements that could potentially add to the game, but in practice they tend to get swamped by the moves and fictional positioning. Whereas with DH it felt like the mechanical elements, particularly the choice of what you were doing in combat, and the resource usage (HP/Stress/Armor/Hope) actually mattered and were significant. For the DM as well due to Fear being a surprisingly limited resource - I had to seriously consider when to spend it!
The other thing which I felt differentiated it from most PtbA games I'd played was that, weirdly, mechanical resolution of stuff out of combat seemed to be actually faster and smoother - not something I expected - an awful lot of PtbA games have a like "Roll the dice then look at this list specific to that move" (and sometimes you also have to work out which move actually applies) sort of approach, which I didn't realize was taking up time and/or being clunky but apparently was. DH uses this 5-position resolution system for everything, with no specific moves (success with hope/fear, failure with hope/fear, critical success), which doesn't require all this looking at lists and deciding which thing(s) happen or what you want to know or the like. It's slightly more simplistic but also somehow slightly
less limited and smoother? I think for precision evocation of very specific moods and themes PtbA's specific moves are ahead but for a fast-moving heroic fantasy RPG? This is a better way. Or at least that's what I think right now.
My mental boundary for D&D variants is somewhere near but probably including Dungeon World.
I think this is too broad to be useful for discussion. Dungeon fantasy or heroic fantasy? Sure.
But by your logic I can call Earthdawn a D&D variant because it aims to build a game in which D&D tropes make sense.
I can see where both of you are coming from here but I'm not entirely sure there's a meaningful difference in your positions. Like, in DW a "D&D variant", strictly speaking? I mean, no, it's not, it's a D&D-inspired game with very distinct rules and structure, but equally, Earthdawn, whilst I don't think either of you would call it a "D&D variant", literally only exists (as you say) because it's an attempt to like, "rationalize" or "fix" D&D, tie D&D-type tropes into the actual world more, in some of the exact ways Eberron and 4E D&D did over a decade later. Neither of those games play out exactly like D&D in practice either (in fact they're about equally distant, in different directions).
(DW was also a bit misleading because whilst it did an aesthetic appeal to "what D&D was like when you were 12", the actual design and functionality was a lot closer to modern, heroic, 4E/5E D&D than either 1E dungeon crawling or 2E low-end heroism.)