Jester David
Hero
You're including UA but not the accessories from 3e and 4e?This is an exageration, 1st edition had (between the PHB and UA) 13 classes
2nd edition, on core books alone 9, but the seeds to extrapolate dozens of specialty priests and other 4 specialists (they weren't fleshed out), further supplements added Barbarian, the so called dozens of specialists and even runecasters, but let's be caritative and consider only 13 in the core book. 3.x sinthetized all to 11 classes, 4e had 16 classes considered "core" (the ones that made it to the srd). The current playtest? 9, ten if we count the upcoming bard, adding two more classes (sorcerer and warlock) isn't going to bloat anything.
Everything was core in 4e. They might have abandoned the SRD but that does not mean the classes in the PHB 3 or side books were not core. 4e had at least 26 classes. And that's including all the disparate versions of classes like the fighter as one. But I'm sure I'm forgetting some.
You say adding two classes only brings it to 10. True. But if we're pulling the sorcerer and warlock out what about the artificer? And the psion has much more of a legacy.
And if they can do that for the arcane classes, why not the warlord? Or the assassin, which has been in three editions or so.