Ok, I read this thread when it was first posted because I was having similar problems, and I finally just solved it for myself, and it was completely unintentional!
Just doing some RHBH driving field practice and purely by accident I held the disc very loosely with just my thumb and pointer finger, and was basically doing a very loose and light version of the forehand hammer drill. After doing that a few times I just wrapped the rest of my fingers around the disc as it snapped back into my palm, then proceeded with my drive.
Instant snap+distance, and I really felt the disc rip out of my hand for the first time in what feels like months!
Amazed, I repeated this a few more times with the same results. What I think I've determined in that in addition to loosening up my wrist and grip is that this changed the position of my thumb placement, moving it a bit closer to the edge of the rim than where I had been placing it.
Before I had been carefully following the instructions we see in all the instructional videos for the pros, carefully wrapping my hand around the disc in the power grip. This usually left my thumb about 50/50 over the spot where the flight plate meets the inner edge of the rim.
With this new method, I'm actually a bit closer to 70/30, with the 70% of the thumb pad being over the wing of the disc, and only 25-30% being over the flight plate.
My fingers also feel more natural on the bottom of the disc just falling into place instead of being consciously wrapped around like I had been doing.
Not sure if this would work for anyone else, but for me it was an instant game changer.
Off to play a couple of rounds, if there is any interest I could do a short video later that shows what I'm doing.