Thanks for your answer. You're correct, I want a playable modulation. I like using the mod input because of the W-30 joystick -- it's got left-right for pitch bend and up-down for mod. There's lots of travel for the pitch bend, but not much up-down travel for the mod wheel, which makes it less flexible in many ways to a normal mod wheel, but for performance, sometimes the on/off nature of it is just what I want. I can map left-right to pitch bend as you suggest, but that's not the performance style I'm after here.
I don't understand why the lag is there, given the oscillator can jump about without glide (e.g., playing different octaves with glide off, or with the arpeggiator), it is evidently able to respond to immediate pitch changes from other controllers. Perhaps it was modelled on a Mini that someone had spilled syrup on the mod wheel :-)
I am new to these forums, are they read by Arturia support, do you know?