I like your “tiredness” idea, but as a hardcore player I wouldn’t be able to interact with that system because it’s tied to dying.
There used to be an MMO called TERA that had “stamina” system. If you died, your stamina was emptied, significantly reducing your life, mana, etc. But it also slowly drained if you fought continuously for hours. You had to take a few minutes break by a campfire to recover. It was neat.
But I have nothing against durability. It gives me nostalgic feeling of Diablo 1 and 2.