I dunno, I'm using a 15-year-old Yamaha DTX kit as a controller for AD2 and I think my snare and high hats sound incredibly realistic with all kinds of subtlety and nuance. ...That you'll never hear in a mix. ;P
I agree that I had to cobble together a bunch of different parts from multiple kit packs to get what I wanted. I think the main things I tweaked was the velocity curves and the pitch and adjusted the room/overhead mic levels a bit.
When I first started messing with AD2 I would have totally agreed with your critiques, The kits felt kind of stiff and stale. But to be honest, in the end I spent 1000% more time adjusting the pad settings on the DTX than the settings in AD2. For me, that was the key to the whole thing. AD2 was doing a fine job, it was my pad settings that needed more attention. What worked okay for the onboard sounds for the last 15 years turned out to be woefully inadequate for AD2.
I've been considering upgrading the DTX brain and snare/hh pads just to see if it is even better than what I have now! :)