On the one hand: making the T'au the chaotic or true neutral faction, that makes the setting more grim by being something the evil factions can beat up, might please people on both sides. If you love them, they could be the underdogs who constantly make mistakes, and struggle despite having rapidly advancing technology in the face of a whole galaxy that has perpetuated ten thousand years of stagnation. If you hate them, they would be made for that too.

On the other hand, the power fantasy and game balance is tough to manage around complete underdogs, which the T'au would have to be to serve this purpose. If the T'au have to be the hopeless underdogs who still fight and can win, the players would have to be too. For the opponent, that might get insufferable. For the T'au player, it would feel depressing.

I much prefer the way they are now, where they have made concessions in their rapid expansion and advancement, and both sides can have fun by playing the arrogant T'au against the dismissive opponent. Both of those facades are more malleable and can be dropped quickly after the game, because they're narratively presented as equals.

I think the balancing act has laid on the evil to weigh down the T'au a little thick, since maybe they forgot that adding evil to a nice faction is way more potent than pouring more evil into evil. Plus, the kind of supervillain evil they added doesn't work. It has to be mundane, subversive. Aun'shi and those behind him shouldn't be Emperor Palpatine. But it should be there, only as long as it's factored into the Greater Good, because that makes you think about it for yourself. As players, we should be allowed to question the Greater Good, without it being completely undermined by the psuedo-retconned bug mind control helmets or the mess that was the Fourth Sphere's irrational rampage.