I have both. Campagnolo mechanical on a gravel / adventure bike, and Di2 on a road bike.

The Athena 11 right shifter (Powershift light action) has already failed, after less than 3000 miles. So I'll swap in a replacement Ultrashift body this winter. I liked the Powershift, it has a pretty light action, less than my old Veloce 10. I think the Ultrashift will take more finger and thumb force, comparable to the older 10 speed shifters.

The Di2 is just like clicking a mouse, with two paddle buttons next to each other on each shifter. I often just reach down with my ring finger to shift, and have even used my pinky when I'm holding the top knob of the shifter with the palm of my hand, and resting the side of my palm on the base of the shifter.

The rear shifts are instantaneous, and the front is fast and precise, and it auto trims the front as you shift the rear. I shift gears way more often, just because it's so easy.

If your fingers can tolerate the (mechanical) braking, then the Di2 shifting would be no problem at all. And you can reach the buttons with different fingers, from all kinds of hand positions, which might help, too.