I agree completely, spells like flames have an entirely different tactical purpose from incinerate/firebolt - short range (and preferably higher damage) versus long range, both in turn having a different use from fireball, which is ranged AOE. The lack of scaling makes destruction magic a lot duller than it needs to be.
Scaling would make it too mana-efficient, but there should be higher-skill equivalents you can learn.
If this were really an issue they could scale the magicka cost up along with the damage. Adding a gazillion different, leveled versions of each spell would be a horrible solution though as it would lead to a cluttered magic menu littered with dozens of useless spells.