I sort of agree with Eldest in this regard. I don't think the greater customization and smaller spell list size does many favors. It opens up more opportunity for abuse while reducing the amount of things a caster can do. Or at least, the way I interpreted it would. Given that each sphere only has a handful of spells in it, how would this work with say, the Pyromancer? If he picks Fire, he gets like, 2 fire-related spells of each spell level, having to leave the rest for something else.