Plus while it’s very convenient for tools that support autocomplete of their parameters, but not all do. So sometimes you just fall in the habit of assuming they don’t.
My experience with flag autocomplete is like 90% it completing a huge filename that I then have to backspace annoyedly. Not entirely sure which shell I encountered it on but wow. I just can't afford to rely on it because of cases like those.
This makes me wonder why shells don't support a simple "undo". Though I think there will be a UI conflict between "undo autocomplete" / "undo paste" / other stuff that edits the current command line, and "undo the last command" which would need much deeper integration with the tools that get run.
not sure about others, surely if you're using busybox ash this won't work (no line editing will work), but I'm sure most shells have some sort of undo, as long as they have any line editing at all.