If the drop bars work for you on the gravel bike you might want to give further consideration to the drop bar mountain bike. True, it is not the ideal solution, but it works pretty well.
I rode mountain bikes with flat bars for 30 years until I developed arthritis in the base of my thumbs which was excruciating, especially on steep rocky descents with lots of braking. I found that drop bars solved that problem because of the radically different hand positions. An old friend built this drop-bar specific mountain bike frame for me. Not the same as your wrist pain but the solution may be similar.
Brent