Crab, Perhaps the collective to pitch attitude aerodynamic coupling is being underestimated, ( not to ignore the inherent rotor dynamics you mentioned ).
Best example I can recollect:
Original UH-60 prototype flew with a 60 sq ft. horizontal tail. The strategy during initial design was to meet US Army dynamic stability req'ts with only a pitch and yaw fluidic SAS. That later changed for the test machines, but the tail was designed around that idea.
Data point: in steady state autorotation at 120 KIAS with that tail ( fixed of course at that point ), the cyclic was almost on the aft stop, and the aft flapping was such as to result in contact with the aft damper stops. Has the feel of taking 51 cal hits. ( Just to be straight with this discussion: the inboard damper attachment point was the preceding hub arm back then, so the damper saw, and was exercised by, any steady atate flapping present. As a result, a damper attachment standoff was incorporated into the head, and that remains to this day ).
Couple of months later, the FBW stabilator was installed, and one of* the control laws integrated into the stabilator from the start was to uncouple the machine, collective-wise. This worked perfectly and resulted in no or minimal longitudinal trim shifts whether the collective was moved fast or slow, large trim shift or small.
* Once the decision was made to use a stabilator, all of the HQ and performance engineers jumped on those opportunities, as you can imagine, but that is another story.