I have a programmable keyboard which I have bound underscore to LeftAlt+N, input with my left thumb + right index fingers. The first key is functionally not a Left Alt key, it is a layer key that shares the same position as where you would find a Left Alt key on keyboards.

But you do have a point because not everybody has access to programmable keyboards almost all the time. Maybe snake_case isn't that ergonomic now that I think about it, although I find it easier to read than camelCase.

Ultimately, the winner is still kebab-case, which is both aesthetically pleasing and is not a double-pinky keystroke!