Grav,
some answers:
I imagine this is why hydraulic failure can result in such high cyclic forces for larger machines with say 4% offset hinges. Actually, most of the problem of trying to manually fly a helo with hydraulics off is due to the natural pitching moment of the airfoil section used. As we get sexier with those airfoils, the pitching moment gets harder to control with human power, so we need hydraulics. The old 0012 was sweet in the moment department, but a poor lifter. That is why the new Carson bladews lift so much more than the old 0012 S61 airfoils.
how does D3 affect flapback? It makes it less, because as the blade flaps, it dumps lift due to delta 3.
I can understand about the need to reduce collective pitch when encountering lift though. Actually, it has the opposite effect, as you increase rotor thrust with back stick, the delta 3 washes it out, so you have a weaker pitch-rate to load factor sensitivity with delta 3 (that is also why it makes the ride smoother!)
I had also wondered about the S-76 twin bi-filars, but finally put it down to the need for increased pendulum mass. Is one tuned to N+1, while the other tuned to N-1? The two bifilars are n+1 and N-1 in the rotating system, and pure 4/rev in the stationary system. The N+1 is sometimes deleted, it is the less needed of the two.