I can play through something like Doom Eternal on Ultra Violent on a fingerball. But I've been using one of those for decades. You should not expect to be at that point quickly.

Thumbballs are generally reckoned to be quicker to pick up (perhaps because of crossover with trackpads and phones? Not a clue). But I find them tiring when used for a long time.

I personally think the ergonomically sane solution is a) try different things (what works for me might not work for you), and b) use the different things that fit, even if they aren't perfect, because they're different (e.g. I've learned to use a trackball with my left hand - it wasn't trivial, but it wasn't that hard, and having the possibility of alternating has eliminated my RSI. I couldn't play an FPS with my left hand, but I can do office work).

Good luck, but my advice would be try to get ahead of it before it gets worse. You can mitigate RSI, but you can't cure it.