You've conflated
skills and
classes.
A warrior has to waltz into a room and eat damage until everything is dead.
I think you mean a character using a melee skill who has foregone Conjuration, Illusion, Sneak and Archery does. A "Warrior" could just as easily pull out a bow and never enter the room, train Illusion and paralyze the entire room, train Conjuration and summon a Frost Atronach to take the damage.
If he couldn't front-load a ridiculous amount of damage he wouldn't last very long.
He would last longer with that tactic than anyone else.
A mage, on the other hand can summon minions, turn enemies against each other, heal, shield themselves, fear, set traps and any number of other things.
So can a Warrior, Thief or Archer. There are no classes, you're using arbitrary names and presuming, wrongly, that it somehow precludes them from using any of the aforementioned spells or skills.
Not to mention the larger variety of ways a mage can deal damage.
Melee and bow attacks have access to a variety of poisons and enchantments.
Being able to put out focused damage that's comparable to melee classes on-top of everything else would be ridiculous.
It's not a matter of putting out the same damage, it's a matter of the damage scaling
at all. At level 50 there is absolutely no reason to ever cast a Destruction spell, you might as well be unarmed.