I just want to note that Jellyfin MPV Shim exists and can do most of this MPV stuff while still getting the benefits of Jellyfin. You're putting a lot of emphasis on Plex-specific limitations (which Jellyfin doesn't have obviously) and transcoding (which is a FEATURE to stopgap an improper media player setup, not a limitation of Jellyfin).

Pretty much every single "Pro" is not exclusive to pure MPV vs. Jellyfin MPV Shim, which mainly leaves you with the cons. Also as another commenter said, I set my Jellyfin up so that my friends and family can use it, and that's its primary value to me. I feel like a lot of this post should be re-oriented towards MPV as a great media player, not against Jellyfin as a media platform.