For what it's worth, I broke both of my elbows back in '82 (radial heads). I can't straighten my arms completely, and rotating motions can be achy, sometimes painful.

I ride a bike with 6500 series Shimano shifters. Compared to the Sram shifters I have on one of my other road bikes, the Shimano shifters require a lot more rotating motion and force than the Sram shifters. It's the brake lever shifter on the Shimano - it just requires much more full hand motion to move to bigger rings or sprockets than the short finger-only motion of the Sram shifters. Shifting the Shimano actually causes me slight to moderate pain (worse on cold mornings) while the Sram is care free.

So, I can see where you're coming from, and the only solution I've come up with is that for me, the Sram system is much, much better.

Another idea is swap your Shimano shifters for Microshift. They're fully compatible with Shimano derailleurs and have a significantly different method of shifting. I haven't tried them yet, since I can put up with the Shimano, barely. I'm sorely tempted to switch over to try Microshift shifters. The other option of going with Sram, I wouldn't do with this particular bike, but would recommend you consider. It would require changing the derailleurs too. I won't do that on this bike because if I switch the bike completely, it will be Campy since it's an old Italian steel frame and it would have to be Campy of course!