As far as I can tell plex only wants separate folders for different kinds of media and file names that give at least some clue to what it is. Plex is much more lax.
The problem with Plex is that is has a very opinionated system that ignores how things are in real life.
One example I can point to is Stargate SG-1. Episode 1 is a two parter and depending on who you ask it's either Episode 1 and 2 or Episode 1 which causes all subsequent episode numbers to be thrown off by 1 depending on how you count.
This confusion is further complicated by the release order on DVD/Bluray, the order of airing, and the fact that all of these things can be different in different regions of the world.
That has more to do with TheTVDB than with Plex itself, and it's really nothing compared to what Jellyfin demands. Plex at least supports several different alternative directory structures and file naming schemes. In order to transition to Jellyfin I would have to rename thousands of files to comply to its specific requirements, whereas Plex was mostly okay with the way I had organized my files offline.
I actually discovered the advanced item ordering menu where can you change the series episode order source, it solved this exact problem for me yesterday
It's a big deal because there's no rhyme or reason why it's one way or another way in different series so when you ask your TV through voice command to "Play Season 3 Episode 2 of [Show] through Plex] and then your TV plays the wrong episode it becomes a big deal.
One example I can point to is Stargate SG-1. Episode 1 is a two parter and depending on who you ask it's either Episode 1 and 2 or Episode 1 which causes all subsequent episode numbers to be thrown off by 1 depending on how you count.
This confusion is further complicated by the release order on DVD/Bluray, the order of airing, and the fact that all of these things can be different in different regions of the world.
And that's just one show.