so far in my cRPG experience (planescape torment, baldur's gate 1,2, neverwinter nights 1/2/motb ), properly leveled, pure magic users outclass melee and rogue build. they can support, heal, and launch a barrage of god-level attack. even with slow agility, low endurance, a simple haste and armor spell can make them decent in surviving, maybe not tanking like warriors or paladins, but you can take some hits at least. with high-leveled armor / haste spell, you're practically untouchable, then there's summon, morphing, time-manipulation,etc etc.
after playing mage in baldur's gate 2 i can't go back to being a puny warrior or rogue. in most of those games, my strategy is basic lure to tank/rogue with backstab, the rest of the mages heal and burn.