Alright, let me lay out why destruction magic is not very fun to play with as a logical argument:
First: Premises you have to accept as true to see this argument:
1. The only ways to increase the damage of destruction spells is through potions and perks.
2. Perks will increase destruction damage by up to 50%.
3. Dealing damage through weapons can be permanently increased far more drastically through their perks, skill increases synergy with sneaking, enchanting, and weapon improvements.
4. Weapon damage can also be temporarily increased by drinking potions, so magic has no advantage there. (Also guzzling a potion before every fight is few peoples definition of fun, but that's more an observation than a fact)
5. Many enemies in the game get stronger as your level increases.
6. When you gain more powerful spells you don't get an improved version of your old spells usually.
7. The more damaging the spell the more costly it is to cast.
8. Magicka does not regenerate very quickly in combat.
9. Skill increases and Enchantments will reduce the cost of spells. Stacking enchantments can reduce it to 0 magicka.
10. Destruction spells can chain stagger opponents.
Alright, if you agree with all of those statements, then we can draw some conclusions from them:
Conclusion one: There is a hard cap on the absolute maximum number of damage you can do with a destruction spell that is relatively easy to reach, but enemies will keep scaling up well beyond that point, meaning that the amount of damage you inflict relative to an opponents hitpoints will begin to decline as the game goes on. The same applies to weapons, but since weapons have more ways of increasing their damage they can keep pace for longer.
Conclusion two: The only thing you can increase after you have maxed out your destruction damage is how many spells you can cast. You can create enchantments that allow you to cast an infinite ammount of spells, but this appears to be more of an exploit than an intended mechanic since it renders the entire magicka system as well as all the dozens of other ways of decreasing spell cost, and higher cost for better spells pointless. Also every levelup you ever sunk into magicka is wasted.
Conclusion three: Since your damage will begin to be relatively low as you progress in levels it will take more and more spells to kill an enemy, even if you have used the 0 cost enchantment exploit. Killing an enemy will begin to take a very long time.
Conclusion four: Since you can chain stagger opponents they cannot fight back, even if it takes a really long time to kill them. This makes fighting as a destruction mage extremely boring, as there is no challenge to winning, but at the same time, every fight takes forever. Fighting without chain stagger is possible, but not very satisfying either. since you have to land so many successive hits to kill an enemy it gets bothersome if they aren't immobilized for most of the fight.
Conclusion five: If you have a favourite destruction spell (For example Runes) that isn't a master level spell you never get to do master level damage with it, so which spells you get to cast if you want to be effective is highly restricted by the fact that spells don't rank up along with you. If Flame is your favorite spell to use the game simply doesn't give you the opportunity to keep using it unless you want to do even lower damage than even high end destruction spells will do.
Conclusion six: If you don't use the 0 cost exploit you will eventually hit the point in the game where you simply cannot defeat an enemy encounter before you run out of magicka. At that point fights will start taking easily five times longer than before, and start consisting mostly of running away while you wait for more magicka, or getting killed horribly because you most likely won't have very high hitpoints if you heavily invested in magicka.
So there you go. That's why destruction svcks. It's primary lifeline is a cheesy exploit. If you do use the exploit you might become damn near invincible, but you won't have any fun with it, since the only challenge left at that point is landing a first hit, and not messing up while pulling the triggers simultaneously.
One sidenote: Since it's relatively easy to evade dragons while you regenerate magicka destruction is one of the best ways to kill them, even without using the exploit. Enemies that can't be thwarted by cowering behind a rock are not as easily dispatched.