In the case of a four-player high-difficulty dungeon, there is much less room for players to work with when it comes to party deaths or mistakes. If even a single party member is incapacitated or makes a mistake, it will invariably lead to a wipe, with not much leeway to save the run or come up with a creative solution.
That's....the entire point of tough content.

It's like saying that adding peppers to a spicy dish is to be avoided, because it might end up spicy.