VIM started flirting with giving me RSI issues (mostly : and esc keys; yes, even on capslock. I have small hands) after some years. It's a comparison certainly but not a control.
You may use Ctrl-[ instead. What do you mean about capslock? Mapping capslock to esc?
I’m going to try that with the key left of space, since it feels completely obvious that the thumb is the natural best finger for modifier keys.
Caps2esc under Wayland and I think I used to use xcape under x11 though it's been a while. (caps2esc has a configurable framework so you can use that for a different key and it should work nicely for you)