You know, you've just inspired an idea - if the user has no panes, then the Terminal could probably pass the Alt+Arrow through, similar to the way that Ctrl+C for copy sends a ^C when there's no text selected.

Originally posted by @zadjii-msft in #3729 (comment)

If the user only has one pane (the whole tab), then the moveFocus keybindings should probably set e.Handled(false), so the keys can fall through to the underlying command-line app. I'd bet that would mitigate the need for tmux users to unbind all the alt+arrow keys, since I doubt they're using our panes with tmux.