You're not surprised, right? It looks like a fairly predictable progression:
Shroud: Keep up the haste and fogs, plus maybe some heightened web. Oh and kill those gnolls.
VOD: Keep up the haste and fogs, plus maybe some heightened web. Oh and kill those bats.
The times when a mage could contribute DPS against devils in Shroud or later were uncommon, and depended upon a ring of melees already clobbering the boss. As a melee in these quests, I can contribute simply by moving in a clump with the other melees and swinging around at whatever gets close... but if there's a mage with us, too often it doesn't make sense for him to even bother trying. With effort and luck he can steal some kills, but that's not a true contribution to the party.
The devs will have to try and find a way to fix the problems you experienced, and I tell you, I don't envy them the job. Part of the solution could come automatically when you move on to mobs who don't have so many fire-immune teleporters. Part of their attempt will be adding
non-spellpoint spells to casters, so they can join in DPSing trash without burning points needed for a boss. But it'll take a lot more than that, and some of the changes would definitely have to upset one category of players or another. It'll be tough!
(A few other things that could help would be Dimensional Anchor as a self-buff aura, and something like Energy Substitution or Searing Spell. Aggro scaling by distance threshold could help as well, as could a Intim and Diplo skills that integrate with Hate points. But those topics get very complex very fast. And hey, Mass Enervate!)