> Ctrl asks you to give up a pinky, a home key finger, to execute common chords - far more critical than a thumb

Am I particularly odd for only using my thumb for space?

I use left-pinky to press either the left-ctrl or left-command. This naturally places left-ring on top of shift for ctrl+shift combos on Windows but I usually use right-shift on command+shift commands with right-pinky. Any keys I press on the right side of the keyboard during this cord are done normally since my right hand remains on the home row the entire time, on the left side I'll typically then use left-index to press the other key.

If I use left-thumb for left-command instead then I can only figure a way that involves moving that hand completely away from the home row and for shift combos I then can't reach most keys and need to move right-hand off the home position. If I use right-thumb for right command I end up with the same in the inverse. I guess one could pick the opposite command based on the keys you needed to press after but it seems like an extra thing to remember + still results in more overall movement.

It's funny how I must have typed at least many 10s of millions of keys by now and never really thought about how I type key combos.

It also has the benefit of (mostly) separating OS wide keyboard shortcuts from terminal commands. Copying text is always “CMD-c”, and not “usually CTRL-c, except in a terminal where it’s actually CTRL-Shift-c, because otherwise that would interfere with terminal control characters”