Why would it be a paradox? I'm sure Yugiri isn't the only Ninja, in the entire world.
There's only supposed to be 1 dragoon at any one time....but that's not how the game works.
For Rogues...well you simply were part of the ROG guild, before 2.2 events. As for Nin..well, you were nin before Yugiri arrived...
Or you meeting Yugiri, to become nin, takes place at roughly the same time as 2.2 events, even if you personally haven't gotten that far in the story. You don't necessarily have to follow a strict chronological order. Happens quite frequently, that authors write stories, where events are jumping around in different timelines. There's some movies, where everything happens from ending to beginning. In XIV, we're jumping around a lot to, with echo scenes.
So if someone is starting in 2.4, you can simply call their 2.0-2.4 journey, as flashback, and becoming ninja, is current time.
Lots of ways to resolve the issue
