I had never considered until now that my left thumb never touches the keyboard.

I think having Shift available for the thumb would help a lot (in the middle just below Space bar).

Most experimental layouts that add more features make the mistake to overload it, some of these things even look totally thumb-driven.... This make everything very confusing. Just Shift for a start, would be good. The pinky is too much overloaded. Offloading some of it to the thumb would actually be an improvement.