I perfectly agree with everything you just said, precise control with the rudder is very important as anyone who's tried to strafe an Ural or something with a P-51 knows.
I feel that precise rudder control is difficult to achieve with a twist stick.
I suppose my point is that an aircraft with a large degree of P-factor will be more difficult to precisely control at least in the yaw axis than an aircraft with a small degree of P-factor.
I don't actually know if that's true but my reading on the Griffon engined spitfires appears to support my assumption.
Your point about changes in airspeed being more important than counter-acting P-factor is well taken, I think you're completely right.