So, to summarise:
Magic users have far more diversity & resources at their disposal, far more in the way of tactical advantage. And yet, the only thing that seems important is that they cannot whack an enemy as powerful as a warrior can.
Different gameplay man, different gameplay. Isn't that what TES is all about? I have failed to see any reason why a mage should be able to whack an enemy like a warrior can. I have failed to see why a pure destruction mage build should be a viable option, when a pure 2-handed warrior is not (no armour or anything else etc). I have failed to see how the insistence that mages should tank should be taken seriously. Mages, aren't they the wise guys who are more intelligent than average? I don't see much evidence of that here, only complaining that the game isn't built for them.
There are many solutions brought forward, and are yet dismissed ("impact perk is so booooring etc"), The only solution I can offer is: just play the damn game man, within the game's limits. So it's more difficult being a mage, isn't different gameplay what we want?
I see a large portion of the forum complaining that Skyrim is too easy, it's possible to OP yourself easily. I see another large portion complaining that mages cannot achieve the same OP potential. Whatever.
Pure destruction build refers to only destruction AS A COMBAT SKILL. There are 5 combat skills, destruction, conjuration, 1h, 2h, archery, and 4 out of 5 can do decently by themselves -provided of course that the player has invested in other defensive or utility skills as well. But destruction is useless by itself, at least until you reach high levels... when I invest in destruction perks, robes etc, fail to kill even the weakest Draugr, then just conjure 2 swords and charge screaming "Victory or Sovngard!!!" and butcher them all with minimal effort - and mind you, no armour and no 1h perks - then something is majorly wrong with Destruction.
And getting OP at late game is ok - yeah, you're the mighty Dragonborn that put down a god-Dragon, of course at high levels it's normal to be OP... but a Destruction mage cannot be as OP as the other 4 damaging skills... for example, an archer could have enchanted their gear with a total of +800% archery and +200% stamina regen, and with archery and other skills/perks that means that they can fire arrows doing 1000 damage each, that will stagger any enemy they don't 1-shot, and -paralyze any enemy they don't stagger for like 10 seconds, WHILE IN SLOW MOTION!. Do that with a destruction mage...
Destruction should be as good by itself as it is coupled with other magic skills, in the same way that 1-h by itself is just as good as 1-h coupled with a shield... But it isn't...
Also, mages don't have more recources than melees... a Destruction mage is about as good in restoration/conjuration etc as a thief or an archer, and has pretty much the same spells as they do...