You are getting them backwards, Virpil has separate controls for pitch and roll adjustments. As far as I can tell based on pictures, i dont see any options to adjust the VKB gunfighter base.
Either way it has nothing to do with the controller, all other planes in DCS and IL2 work just fine, it's the way the Spit IX is modelled in DCS that is hypersensitive to inputs. Anything within the margin of error while holding the stick striaght will be very noticeable. I'm not trying to convince you, i'm just sharing my experience.