well, i think they are. Specially against necrons and IG, the good old skyray can unleash a real hell down there with their barrages and so.
Also the fire warriors and stealth teams once fully upgraded they DO REALLY kick some butts. In soulstorm the thing goes far worse as the barracudas are way too powerfull for an air unit (they can criple any tank or building in seconds, greatly suplementing Tau infantry). Also the hound packs are way too strong (250 DMG!!!) and if go for mont'ka one can get up to 2 Hammerheads and the crysis suits with flamers (that are actually mobile moral breakers).
Seriously, if DOW3 is going to come with Tau within (please not another expansion of DOW2 that game sucks), GW shall nerf them a little bit.