IINA is much more than mpv. Sure, it uses mpv underneath, but the selling point of IINA is a well thought out UI with just enough features but not too many (totally subjective, of course)
> ...the selling point of IINA is a well thought out UI with just enough features but not too many
That's exactly how I would describe the default mpv UI :)
I do use both — I actually used MPV before discovering IINA — but I like the UI of the latter, even if I still use MPV keybinds.