I respectfully disagree. Tau are the most brokenest army around (save for chaos daemons, but I won't go there)
Further, my experience with XV suits is that if they max out and take drones, they'll lose one and run screaming off of the board, taking their expensive weaponry with them. If they only take two in a unit, if you lose one (you will) they can always attempt to regroup because they are never below half strength, and don't have to buy a bonding knife.
My other experience with stealth suits is that for they points and what they do, I'd rather spend the points on a XV8 suit unit and pour the remainder into a pathfinder squad or sniper drone team. You'd be better off, trust me.
Third and lastly, I am speaking from experience. I PLAY tau almost exclusively, and have tried every option, load-out, and list (save for vespid and skyray because I don't see their benefits when compared to what railheads and kroot do) and I'll say unabashedly and unashamedly that Tau DESPERATELY need a new book. Chaos need a new book, Eldar need a new book, and Tau NEED a new book. Something to put us on par with at least the IG or Necrons.
Just my opinion.