Copied and pasted because it was appropriate.
Well, I just decided to try teching to Dark Armada in a 3v3 game (vs 3 TEC's) and it really is super powerful. Didn't research a single other tech or build a single extra building on my way there. I went from absolute last place with 3 planets getting pounded by my neighbour to taking him out just like that. I then proceeded to amass a fleet twice as large as anyone else and go on a rampage, winning the game with an ally.
It definately helped that two of the three opponents were picking on one of my allies and not attacking me. I think that the best counter to Dark Armada would be early game harassment. So if you're up against Vasari, HARASS! I didn't have a single missile turret the entire game, and lost a planet in the first 20 as a result, but the player couldn't press because my ally attacked him from behind while the other 2 were off hitting the third guy on our team.
As a comparison, I had a maximum of 5 planets that game and the largest fleet as a result of 5 phase stabilizers. One of my allies who was not attacked almost the entire game had a massive trade network, 10 planets, and still couldn't afford a fleet as big. The last opponent in the game hadn't been attacked all game and was also way behind me.
I am not sure what the right way to nerf Dark Armada is yet, and not 100% positive that they need it. To be honest, it's wicked fun to play as, lots of adrenaline as you wonder if you'll last long enough to get them online. I am 100% certain that the best way to counter it is to harass. The last thing they want to do is spend resources on ships or defences, and losing a planet with research buildings is devastating. Right now, if the Vassari player lasts long enough, they WILL win (unless something stupid happens, like their allies leaving).