I don't like using conjuration and I shouldn't have to. That's like saying that "most warriors who use two handed weapons and single handed weapons do fine." They're completely different schools of magic that shouldn't have to go hand-in-hand to use. Destruction has always been a combat specific magic. Now it's worthless.
It's not "only destruction." It's Destruction in combat. Destruction mages use destruction in combat and now it's useless because it doesn't scale to your skill level and the spells are highly limited in their abilities. There was no warning at the beginning of the game that said "By the way: You can NOT beat this game if you are purely a mage due to the fact that destruction will not kill higher level enemies and even if you put the effort into all your magics, you will have wasted your points for not playing the way this game was built for."
That is TOTALLY the point. There are a lot of people getting towards the end of the game who now feel they were deceived. They were told they could play the way they wanted, so they chose a destruction mage who shoot fire and ice from the sky and reigned electricity from their fingertips. In ANY other game, it would be a reasonable assumption that this would be an acceptable play-style for a wizard, let alone a game that promised you that you could be anything you wanted.
They spent hours on the game and found that low-and-behold, they could NOT shoot fire and ice from the sky, and reign electricity from their finger tips; at least not if they wanted to kill anything.
Now they all have to scramble to pick a ball-and-chain fallback skill that they didn't really want to play, because this one particular skill couldn't handle the game at higher levels.
Even if this was the intended function (which I suspect it wasn't. I'm still guessing it was an oversight), it is blatantly misleading. I don't understand how expecting destruction to be useful throughout the game is considered unreasonable. Every mage/wizard in popular culture uses spells similar to what is found in destruction as their bread and butter. Did Bethesda really think that no one would want to play this type of character?
I'm sorry, but I refuse to invest all of the time, money, energy and perks into a COMBAT SKILL, that becomes effectively impotent at level 40. Yes, I can use conjuration to subsidize it, but then I have to level that up to, which I might as well have done in the first place. It defeats the point of destruction all together.
It is possible to play a pure conjuration mage; it is not possible to play a pure destruction mage. Conjuration is not a supplement. It is a fall-back. Unfortunately, it is a VERY NECESSARY fall-back for a very broken skill.