My issue with the terminal is the exact opposite, everything is monospaced, hard to read, and space-inefficient due to that. Keyboard use is not a terminal-only thing either, it's a problem with some modern UIs that are hostile to power users. I feel it's at least partly because power users that create their own tools removed themselves from serious GUI development and are too busy with fancy TUI doodads and dark themes instead.
I feel like the point of monospace is to be easier to read in text dense environments. I find it much easier to read a monospaced font in the terminal and it makes editing commands much nicer to work with.
The point of monospace is easy vertical alignment in code, tables, logs, and many other types of text. But you definitely lose fast visual shape acquisition and potential density of proportional fonts. CLI is fine conceptually, I'm talking about TUI which is different.
