Hussar
Legend
If that's what you think, then I think you have a far, far too narrow definition of grim and gritty. Mid-level party but with limited magic and healing in the game (actually quite easy to do in D&D) and you're still staring grim and gritty right in the face. You can take a few hits but each hit point becomes a precious resource. Name level PCs, in a typical magic-rich D&D campaign, are potent. No doubt about it. But that doesn't prevent a DM from adjusting a few assumptions and playing much more gritty. And it really does only take a few adjustments for the rules to work gritty. Check out the Thieves World supplements for d20. Not many changes, game much grittier than base assumption D&D.
Honestly haven't read the Theves World rules so I cannot specifically comment but in baseline D20 D&D, no wounds can ever take longer fhan a week of bedewt to heal and typically wounds are gone the next day or maybe the day after. So HP as "precious resource" certainly doesn't fit.
As I said, people will make all these claims about the game but almost nver actually back them up with direct evidence from the game.
It's funny. You go back a few years in posts on En World and you'll see almost weekly threads of people trying to do low magic or grim and gritty D&D and not having much success. Yet apparently it's a trivial thing to do it.