On May 21st and 22nd of this year, the Alamo GT took place in San Antonio, Texas, and something unprecedented happened. Tau won the GT! There were some really cool-looking armies present, noticeably several very large models (several Lords of War, FW Superheavies, etc). But, I'm not counting it as a win for the codex or the army (despite the fact that it clearly did). Why?
Because the winning list used 1/3rd of its points on a Forge World KX139 Ta'unar Supremacy Armor. So really, 1,250 points of this list was from the codex while the other third is all in one expensive, large, and very awesome Forge World model.
Now I've used the KX139 and honestly it wasn't very impressive, but that was in an Apocalypse game and it only got a few turns of shooting off, not a full 5-7. So I guess my experience with it is anecdotal. Regardless, if I'm to believe the unjustified, baseless whining people have done over this thing since its release then I'd say that if 1/3rd of your list is one super overpowered model that carries the rest of your army through each game, then no matter what army you play that's not representative of how your army normally functions without access to unbelievably good toys like the Ta'unar.
To play devil's advocate, sure, this is an example of what Tau can do when they have unbridled access to every unit, vehicle, super heavy, and gargantuan creature at their disposal. That directly makes the point that some people were trying to make, but I think people are quick to forget that they lined up with pitch forks in-hand ready to lynch the new Tau codex the day it was released (and with each expansion book like Kauyon and Mont'ka), BEFORE Tau even had the KX139. The claims were that the army was broken, unbeatable, etc, and there was no way around them other than nerfing them into the ground (as if Eldar didn't firmly and unequivocally hold that title since they got their last book lol).
So my point is that I want to see all the data proving Tau are this supposedly unstoppable force, without them having access to the KX139, because so. many. people. whined and complained about something they had no knowledge of and still do to this day. I still see it on the boards and facebook groups, and it's completely ignorant.