First of all, welcome to the 12 Sky 2 community
Yes, it does say that Fujins are weakest, Guans balanced, and Jins strongest but slowest and stuff, but that's more for show. In 12 Sky 2, all factions are the same in every way according to stats. So it really all depends which you like better or think is better. Maybe go with your instincts.
Note: Fujins are the most populated faction with the most masters. We win almost everything. Jins are at the bottom of the factions. If you want to have a challenge in PvP, but more places to grind, join them. Guans are in the middle of the faction ranks. They..uh.. have nice maps? xD.
Well anyway, good luck in whatever faction you pick. Hope to see you in game.