This is only true if you assume that Tau culture is a static and unchangeable thing, that will refuse to accept political realities or an existing situation in any way.
EDIT: In the Cultureverse, Taulikes aren't that unusual. Many many societies are that vibrant and self assured with themselves, but then settle into a more passive form after becoming a powerful and secure interstellar force. The alternative after all, is absolutely horrifying warfare against technological superiors with material advantage.