Of course any 'game' is a balance between realism and playability and too much realism can mire a game. However, RPGs are essentially stories and if I read, in a fantasy novel, that the hero has hit the villain for "2 hitpoints of damage" my immersion in that story is going to be pretty much gone. So why should I be happy with that in the context of a PC game?
To my mind the best combat system I have come across has been in Temple of Elemental Evil but, good as it was, there was no true damage system. Basically every character, NPC and monster fought equally well, with all or almost none of its' hit points, until, at zero points it became unconscious and, I think, at minus 10 HP it died. There was no variation to this, so after a while combat could become rather mechanical. Fortunately it was spiced up with other elements which went someway to keeping things interesting; for instance, taking potions in combat could provoke opporunity attacks from nearby enemies.
Damage recieved or given in combat combat is, or should be, as a result of getting something wrong or right. So if combat , in a 'mature' PC game is going to have any real meaning, it need sto have potentially bad consequences. Some damage should not be able, in every circumstance, to be fully healed. And, while in combat, damage taken should have possible negative effects, even if only for the short term of that actual combat, irrespective of spells potions or kits (which, from a realism perspective should really only be applied post-combat).
Without some form of damage system will a modern, gritty, mature fantasy RPG be any much different from playing Zelda?