For me it’s a trade-off: yes Plex is less good than Jellyfin from a data/cost perspective. But so far the UI of Plex (which is not perfect mind you), availability of Plexamp (which honestly is very very good), and the fact that I don’t have to pay for it anymore after buying lifetime swings the scale towards Plex for me.

If Plex somehow canceled my lifetime or forced ads on my shows or something, that would be a line — but making me opt out of selling my data is not that line for me.