there can be more than one heartbreaker, also do you have any evidence for your DC20 claim, or is it basically the same you accuse the DH critics of?
I'd not seen DC20 before, but looking at it, it looks like an absolutely classic modern take on the "Fantasy Heartbreaker" in that:
A) It's targeting the exact same audience as D&D.
B) It claims their rules are "better", and I can't comment if that's true or not, but they're clearly as complex as 5E 2024's rules, and don't, fundamentally, appear to offer anything very different to them. They do seem to have enough differences to active the "heartbreak" aspect if you like those differences though.
C) The tone and subject matter of the game seem to identical to D&D.
D) It doesn't seem to have some kind of overwhelmingly popular brand or IP or the like associated with it.
Like, even a random OSR game looks like less of a "Fantasy Heartbreaker"!
B, C, and D are not true for Daggerheart, or massively less true. And A is arguable at best for Daggerheart. Daggerheart may succeed or not, but it's not a "Fantasy Heartbreaker", because, fundamentally, it's not just "My D&D is better than official D&D!".
Note that success is part of what ultimately defines a "Fantasy Heartbreaker" - if DC20 is extremely successful, it will retroactively become "not a Heartbreaker". That's how it works. Fundmentally Pathfinder had basically all the characteristics of a Fantasy Heartbreaker, except kind of D, because it did have a pretty popular brand associated with it. However, it hit at a very tricky time in D&D's history, when a ton of people had a lot of unplayed 3.5E material (often much of it Paizo adventures), and 4E had proven very divisive, so it managed to succeed. Maybe DC20 will, but I think it's fair to call that a potential "Fantasy Heartbreaker" based on their website and PDFs, whereas Daggerheart is just a fantasy RPG, not a Heartbreaker, because it's not just a "My D&D is better" game.