As a dedicated Jellyfin user, 100% agree. I love it, but glitches where it loses my seek progress and requires restarting the video, or the terrible subtitle support on Roku, or the often lackluster library management (they improve it slowly though!), and more I’m sure, these all make it much harder to recommend.
It does have a Roku app, but it’s very limited in features and barely developed. It will probably work if all your files are x264 in your native language, however it doesn’t work for my use case. I tried playing some anime encoded with x265 and it was unwatchable for me because:
A. The TV could not handle the decode and there is no (sensible) way to force server x264 transcoding for just the TV, and:
B. Selecting subtitles and audio tracks is painful and sometimes impossible. I tried changing my Jellyfin settings, my Roku settings, using the selectors on the episodes, even setting the default tracks in the video files. Nothing worked to have dual audio or dual subtitle files play the correct tracks.
I can’t speak for any other ecosystems, only Roku.