Honestly, I don't get it. This idea of "balance" is like, I dunno, some kind of disease. I don't like it.
The game isn't "broken" because certain kinds of mages are harder to play than others. Where is it written that a "pure destruction" mage should be exactly as easy to play as some other kind? I think it's fine to have a rough balance between the main archetypes -- melee, magic, stealth -- but if you choose to specialize in only one kind of magic, why *shouldn't* that be harder?
All these comparisons between Destruction and Conjuration -- who cares? Either spend some points and perks on Conjuration, or pick up a few Summon scrolls, they're easy enough to get. Choosing to be a "pure destruction" mage is a *choice* -- like being a warrior but deciding to only use daggers.
You might call it "balanced" if all character builds were perfectly balanced with each other -- but I'd call it "boring". Lord, how I miss the days of EverQuest (the first one), where the game would actually tell you "hey, great that you want to be a troll healer -- but please note this kind of character will be a lot tougher than most others".
I vote for *less* balance in future games, thank you very much. It'll give the min-maxers something to do, the complainers something to complain about, and the rest of us some actual replay value for once.
Incidentally, I'd also like to vote for quests that are actually class-specific. In skyrim, I became arch-mage entirely by accident, while being able to cast nothing besides novice/adept spells. I'd love to see that change in future TES games -- doesn't anyone else remember how many different factions there were in Daggerfall, and how you couldn't just join all of them???
Game isn't broken, but combat
is broken if there's no balance. Appropriate degree of challenge and a reasonable selection of viable and enjoyable play styles is not a bad thing. If you don't care about combat, that's fine and you'll enjoy the game regardless, but for people whom combat balance is important - and it's especially important for replay-ability for me personally - it's not a disease, that's just a sensationalist way of describing it and it's complete nonsense.
Destruction gets complained about, and it's completely justifiable that it does, because it's the core of a popular mage play style. It's like making swords a terrible option for warriors - most people who play warrior type characters just aren't going to be happy about that for good reason. And being a warrior who only uses daggers is a bad anology because you can perfectly well play a warrior which only uses daggers and there's no reason you shouldn't. You sacrifice some damage and range for speed. It's a reasonable trade off. Specializing in destruction instead of conjuration isn't a reasonable trade off - it's a clear loss.
It's also a red herring to suggest pure destruction being non-viable relative to destruction in combination with other things because that isn't even the issue. Destruction just isn't good no matter what other skills you mix it with - it's a bad choice for a way to deal damage. The only exception is if you use 100% cost reduction, which is clearly not a good or balanced solution and is counter-intuitive to perk tree design since so much of spell school related perks are made obsolete by enchants.