KidSnide
Adventurer
In general, the "non-core four" should be narrower, both mechanically and flavor wise. A paladin should feel more specialized then a fighter, a druid more so then a cleric, etc.
I don't think there is any question as to whether the sorcerer should be narrower than the core four. Of course it should be. The issue is that it is so narrow that it doesn't cover many concepts that have traditionally been covered by sorcerer classes (i.e. any type of inherent magic that is under control and/or doesn't transform you as you expend spells).
In comparison, it's like a paladin class that only works with gods of the sun, or a druid class that can only turn into a jaguar.
-KS