Dlna works really well for me... on linux with a PlayBin media renderer. Which will support essentially any media thrown at it. I've definitely found tv's and sticks to be very hit or miss eith codecs, need transcoding too oftenm But dlna worked pretty nicely when I used it with a competent media renderer.
The appeal is being able to have some network connections to other people's media servers too. Making the media server less of the primary focus is a shift, & handling media-providers as replaceable modular systems would be a step up, & is essential for group-usage to evolve; something we technically cant really do effectively now.
I do very much see your point that Jellyfin has a lot of good capabilities for media-watching. I'm stillfeeling strongly like media providing/serving is a different role tham media consuming, that many of these responsibilities could shift to a more local-centric android or tv app that expects you to have used general file sharing systems to coonnect up.
Good discussion thanks. Shout out to the other mention of transcoding, which definitely plays a part too. Setting up a fuse mount to transcode your stuff to a given quality & them file-sharing that too would be doable & still "generic" versus a specific media-sharing system like this, but yeah, it's more into the cobbling stuff together realm.