Then there must be a lot of confused adventurers out there who only rely on, say swords, because obviously swords couldn't possibly be viable offensively on their own and scale with your skill level and gear...
Oh wait that is exactly what they do, that destruction doesn't.
As far as I can see, there are two separate concepts that people are confusing as one.
Concept 1: Damage output
Concept 2: Survivability
What your opponent wants you to consider is that Concept 2 is not part of the issue. Doesn't matter how squishy the character is, we would simply expect that a highly leveled highly perked destruction caster would be similarly capable of damage output as someone who was highly leveled and highly perked in, say, one-handed.
In other words, if two unarmored characters with completely equal defense were to confront some mobs, would there be an observable difference between their offensive effectiveness. The "issue" being raised is that there is a substantial difference, all other things being equal.
Seriously now. All you idiots, yes idiots I'm being very kind here, who disagree that Destruction is not underpowered need to read these two posts. Your inane arguments of: 'Well use another tree', 'You shouldn't be able to nuke a whole room', 'You're supposed to be squishy' show how little you are understanding what is being argued.
It isn't about utilising multiple trees, it's about having the only damage output of a mage being equal to an Archer/Melee character, hell I'd even settle for having HALF the damage output of those playstyles. Example, I can hit harder with an Ebony sword, with NO PERKS in one handed, then using an adept level spell with ALL PERKS. What's worse is that you can increase the output of the sword by simply GAINING SKILL POINTS, this doesn't happen in Destruction. You get the spell, that's it for damage for the ENTIRE GAME.
I caps-locked the more important bits so you 'Destruction is fine' people might be able to grasp the issue
Numpties.