the IRFP240 VMOSFET have way more nonlinear input C - especially near saturation so high VAS current is a good ieda
No real question, no real help. You haven't specified anything--what's the suppy voltage, power level, power bandwidth, exact VAS topology?
It's unclever to drive any power device directly from the VAS. Distortion will be unnecessarily high and there will very likely be some sort of large-signal limitation. Add an emitter follower in between.