I tried virtually all of the tweeners for the very same reason, to find a less stiff and better feeling APDC+. I'd say the only one that gives you similar playability features (easy fast swing, spin-based control, high margin for error, racket seems to do a lot of the work) which is significantly less stiff/harsh are the Donnays. I tried the x-dual silver and gold and both had that super-easy, spinny response, extremely soft, plus a trillion times better touch/feel. Maybe a bit less power but I think the power is there to be dialed in. That said, there was something about the very soft feel that I just didn't like but I think for many it would be a dream stick, it was really impressive. Definitely worth a spin.
Of course there are many APD types that perform similarly and are somewhat more comfortable- Pro Open, Technifibre, 4D AG500 Tour, etc. but I think they are all in the same league of stiffness and over time you still feel it even if they are more muted or solid feeling than the APD. I think these are ultimately lateral moves as far as arm health.
And there are others that are indeed more comfortable but just don't do what the APD does for you with such ease- Exo Tour 100 (not nearly as whippy), Becker (less spin, less whippy), 400T (don't get me started).
Just my findings from trying 100 tweeners to specifically replace an APDC+.