Yeah, VLC is great and has been great for a long time. But the MPV-based stuff is amazing too and just seems faster, cleaner, etc. Which I'm sure is due to being much more focused, just using ffmpeg, without decades of legacy code, etc.
My biggest problem has been that I find nearly all of the MPV-based players I've used (mpv-player itself, or stuff like IINA or Celluloid) either have a massive lack of configuration options, overly minimal UI, or both. On Windows, Mac, or Linux
I don't need integration with some obscure external timing system by default like VLC offers, and that kind of thing. But it's weird that so many players don't offer you the ability to enable basic plugins. Or change playback speed. Or configure keybinds. Or continue playing the next file in a directory automatically. Or even offer the ability to display the most basic info about the file being played, like codecs. Etc etc.
Or in a couple of cases they seem like more of a mess than VLC.