For a Full-Mage Destruction is the only method of attack, and most of the time as a full-mage you spend your time -not- getting hit, either by running away while flinging spells or by conjuring up creatures to tank for you. In the end, you use alot of Destruction spells and gain alot of points in it (so Destruction's skill gain is good, imo), but if you succeeded in not getting hit, you won't need to use Restoration at all.
Idk how it is for you multi-taskers, but this is just coming from a full-mage.
So, should the Restoraton skill take less castings to level up in Skyrim? Maybe equal to Alteration or something...