Take? What take? Plex handles it automatically, Jellyfin does not. That's not an opinion of mine, it's an objective fact. No take. I'll stick to Plex because of this until I'm forced not to.

but it's still work someone has to do, and there's many requested features - as well as maintaining the current feature set.

I mean, sure. It's a community project too, right, so turnaround is even longer probably. I know it's not going to happen at the flip of a switch, I'm a software engineer by trade. I'm just saying that Plex handles this while Jellyfin does not, so I'm going to use Plex until this works in Jellyfin.

I was looking into the Merge Versions plugin, but I'm hesitant to use it if it means that it'll go into my library and rename all my files. I don't want that. But I couldn't find a description of how the plugin works, so I'm holding off for now.

Sadly there's an internet connection required to login to Plex, which is a no-go for me.

I don't think this is necessarily true? You can manually enter the server address without logging via plex.tv, I believe.