I'm going to disagree with this to an extent, and there's 2 main reasons why:
1. When people complain about the homogenization of classes it's usually because abilities get shared to other classes or removed. Things like Mortal Strike, Curse of Tongues, Curse of Elements, Knockbacks, and even what classes dispelled all use to be unique. Then they get shared, rogues and hunters get MS, then demo locks, curse of tongues goes to hunters, druids get a passive elements, etc.
2. This spell school thing is restricted to just 1 spec as far as I know out of all of the classes' specs. Even demo and destro have two schools. I think that this was more an unattended consequence of trying to make the specs feel more unique. Way back when, affliction had searing pain, rain of fire, immolate, and even soul fire. Then they started making some of those spells unique to specs and got rid of searing pain and immolate for affliction, the latter of which was due to affliction locks in PVE having to manage UA, corruption, CoA, Siphon Life, and immolate. We had fel flame so who cared if we lost searing pain? Heck, it even lengthened UA at one point. They've just slowly been weeding out fire spells and we haven't cared since we had fel flame.
The problem I have with affliction locks isn't damage, it's just how clunky the spec is. It has no bearing on competition, but the class just isn't fun for me, and it's for two seperate reasons. First, when they introduced soul shards they were just a "bonus" for strengthening spells through SS. Then they took haunt off of its cooldown, got rid of the healing component, and said "this costs a shard now!" Now I find myself starved for shards just for haunt in long fights, and if some melee happens to get lucky and gets their interrupt off on me I just sit there waiting/meleeing/wanding them. Ember generation is shit without charred remains now, I have no idea why but it feels like it takes half a minute of spamming incinerate to get an ember. Second, they've tried to "go back to BC" levels of damage/healing and abilities, but back then ferals and pallies didn't have interrupts, and DKs with their seemingly infinite stuns/interrupts weren't around. On top of this we have no fire filler as mentioned previously AND they've taken out a decent portion of our utility. We're just getting the worst of both worlds atm in my opinion.