Firstly, this is not a discussion of Destruction magic's maximum damage in relation to swords/bows, etc. That topic has been done to death on the forums.

My problem is the way in which lower tier spells become utterly useless as you level a Destruction mage.

In all other schools of magic, there is a suitable replacement for each spell at a higher tier. i.e. Oakflesh -> Stoneflesh -> Ebonyflesh etc.

There are NO replacements for the Novice tier destruction spells! Spells at this level offer a unique "flame-thrower" style of attack that is not duplicated by any higher tier spells. In fact, most tiers of destruction magic have a unique spell effect that has no anolog in higher tiers, but becomes rendered useless in terms of damage as you level. Adept tier ranged AOE spells have no higher tier equivelent (unless you count the Master level giant PBAOE spells, which are a different use case anyway). What this effectively does is force you to change your play style at each tier of spells, and removes valuable versatility that you might have otherwise had before. Cornered by enemies in melee range? Sorry, Sparks doesn't do enough damage to help anymore. You can only use Fireball, which will also nuke your melee range companions and summons. Need to nuke a group of enemies from a distance? Sorry, Expert tier spells are all single target, and Fireball's damage barely scratches enemies anymore. It would be as if a melee character was told "Use swords at Novice level, then switch to bows at Apprentice level, because swords no longer do enough damage. Ok, now change to Battle Axes as Adept level, 'cause bows no longer do enough damage."

There should really be either: A ) replacements for all unique spell effects as you level, so that mages can remain versatile or B ) Lower tier spells should scale in damage to remain competitive with higher tier spells. Each spell tier has a use and provides versatility of attack types completely removed from the total damage, and they should remain useful throughout the game.