OK, I think I might need to back up a few steps and work out just how my rig is supposed to function.

I - and my entire physical rig including the two Yamaha KX controllers - predate General MIDI and I've honestly never worked with it.
I'd been going by this legend printed on top of both KXes:

But there's also this table at
http://www.synthmind.com/MIDI%20Standard%20Controller%20Numbers.html which I presume is probably also pre-GM but I assume was folded into it. I guess that the defaults for things like pitch/mod wheel, sustain pedal, and the like in the Arturia plugins follow GM and I need to make sure that the other hardware follows that to avoid having to rework all the plugins in Collection V individually.