Unfortunately Ben, the logic of anatomy doesn’t really allow us to fully relax the wrist without relaxing the fingers. The muscles and tendons connect so much, to where even if you just barely squeeze your thumb and index finger together, you’ll feel the muscles contract and tighten in your wrist. So evidently if you loosen your wrist too much, your pick WILL slip. I don’t know if this helps, but I have a few suggestiions that may help.
1. Perhaps you could try using a different pick. I had to switch picks from a basic fender medium (I don’t know the exact type, I just know it’s slightly thin, plastic and smooth) to a Dunlop Tortex and even a gator grip occasionally.
2. What gauge strings do you use? I use to play on 12’s for rhythm and the thickness made any contact with my pick slip CONSTANTLY. I switched to 11’s and it got better. Significantly easier with 10’s
3. How hard to you hit the strings? I’m a pretty raucous rhythm player, and my pick slips all the time the harder I hit.
4. Unfortunately, it may come down to just regripping it when you can. I use my pick the way Papa Gates shows here now, and I occasionally will make contact with my middle finger and kind of “scoot it back into place”. If you’d like me to make a video of how I do it to better demonstrate it, I’d be more than happy to.
Sometimes I think things like this are inevitable. I actually recall even seeing Syn regrip his pick on stage. Mostly because I’m sure his hands get sweaty, and pick slipping may be one of those unavoidable things we have to learn to quickly fix in a pinch. I hope any of these help. Don’t give up! You’ll get it eventually
SIDE NOTE: I can’t believe how much my singer’s anatomy classes have helped me on this site, lol! She’s a massage therapist and she practically had to go to nursing school of anatomy classes in the beginning. They’ve helped me understand things in so many ways, lol!
