RE: Blade CP main shafts junk brand new?
Honestly, I was of the same opinion as you, but I've had a few problems with it yo-yoing and on another site I saw that one of the likely causes if play in the main shaft, so I wanted to check into it. Definitely I would expect that while in right-side-up flight the aerodynamic torque should keep the whole assembly behaving but others think otherwise.
I'm on my second airframe, so I checked vs. my old airframe and that's definitely got less play in the main shaft, and I'm positive before I replaced the shaft on this one it had less play. I'll still see what I can do about it, a friend of mine suggested I just fill the hold with epoxy, then drill out a small enough hole for the pin and assemble it like that, which ultimately I might try.
All the same, she still flys and responds fairly well to cyclic and collective commands so as long as I'm not grounded I'm happy.