The Crimson Binome
Hero
You might be overplaying the significance of that assumption. Even if baseline assumes that combat healing is available, simply removing that option wouldn't necessarily have a huge impact on most encounters. PCs are already so ludicrously resilient in this edition, largely due to Hit Dice and long rest healing, that combat healing is something which only really comes up during big boss fights. Not having combat healing would mean that they can't bounce back indefinitely during those big boss fights, but you could balance that (if you were so inclined) by fighting weaker bosses, and the benefit is that players might have to engage with easier fights and think more tactically since they won't have that safety net.Thinking more generally: one way to eliminate or greatly reduce "whack-a-mole" would be to somehow curtail or nearly eliminate in-combat healing. Instead of having it as just another fact of combat, make in-combat healing dangerous, risky, and therefore exciting to try; and if nobody wants to risk it then if you're down, you're down until the battle's over. Problem is, 5e seems to expect in-combat healing as a fact of life...grumble grumble dumb design...OK, on to plan B.