Well, yeah true it started like that. But still Jellyfin followed the open source path. I’d expect that under the hood there would be very little left of what was Emby, it was just a starting point. (github.com/MediaBrowser/Emby , before they changed the licensing and removed any further work to the GPL 2 version).
Also Emby is at 4.8.1 now and has been making leaps and bounds in changes lately.
As I said, licensing was the issue for Emby, and the easiest solution was to change their license. It wasn’t just to make money, it was about being able to handle licenses from other software, such as Fraunhofer