I'd also note that it is unnecessary, as one could just have all spells have a scaling mechanic. I'm thinking of something like a per spell metamagic effect, where you have a spell, and you can increase its level to do specific things, which effectively has spells at a range of levels (to use the Fireball example being thrown around, you might have that end up being level 1-5 or so, with a level 1 base spell, up to 2 levels of increase in damage, and up to 2 levels of increase in spread).
On Sorcerers and Warlocks: I'm not liking the whole "class X hates class Y" nonsense this is setting up, and the fluff is a little overbearing, particularly as spontaneous mages are prevalent within fantasy and currently can't be represented well due to the way sorcerers and warlocks appear to be handled. However, both the sorcerer and warlock are close to workable. The core concept of the warlock as someone who has traded something for power is a usable one with precedent in the literature under various names, and if the inner power concept is broadened so that the trapped soul is just a subset of sorcerers, that should work as well.