NPCs don't follow the same rules as PCs, never have in 5e, and that's ok.

[Kuu Lightwing]

So you're suddenly concerned about Enchanter damage output? When the old Volo Enchanter was CR5 throwing out 10d6 fireballs (which they can make your party autofail no less), where was your picket sign then?

I don't think I made any statements about old enchanter at all, have I? It doesn't matter what flaws it may or may not have in the context of this discussion.