Slow healing just matches a completely different aesthetic to modern DnD. If you have slow healing, you end up making magical healing mandatory, otherwise your character(s) get sidelined for ridiculously long period of in-game time, which means you then have to adjust your stories for that possibility.
Or, you end up avoiding combat so much that you might as well not have detailed combat rules because it's a bad idea to have it to begin with. In turn, this makes a class like the Fighter absolutely unnecessary and disposable because it's ONE thing it can do well is to be avoided at all cost... And, again, it gives magical means of overcoming obstacles a LOT of value compared to mundane heroes (which are actually the majority of fantasy heroes, btw).
A game like that s possible, but DnD just isn't that game anymore. You can lament that if you want, but it is what it is. Personally, I think it sounds boring, but I guess I'm not a 'SERIOUS ROLEPLAYER' because, quite frankly, I like a good fantasy tussle and constantly tip-toeing around encounters gets really repetitive.