Overheard people talking about this thread and decided to go look for it. I remember Sinkillr saying something about this a few weeks ago on sins. Although I haven't tried the flak vs cobalt test yet, there might be a little something there.
I remember a 5v5 game in which Sinkillr and I spawned next to each other. I had the immediate advantage because i started with three roid/moons next to me, and two neutrals with crystals, just two jumps away. Sinskillr started with the basic two roid and earth combo. I took my planets and neutral fast, as did Sinkillr. I started with the Marza Dreadnought and corvette spam, while Sinkillr did the main advent start, Progenitor Mothership and disc spam. I was able to kill his Progenitor two times before he finally had enough flak spam, now remember I had the advantage at start with my planets. To counter I made cobalts and this is where it got interesting.
I noticed that when my cobalts were firing at his flak, they had to keep turning as the flak were moving around and behind them. They were clearly taking extra damage, as the disc were shooting them also. By "extra damage" I mean that the cobalts weren't exactly doing damage every second as they would have been while shooting the stationary disc. I kept my cobalts attacking the flak for awhile, but noticed that I wasn't doing as much damage as I could have been doing if I had been attacking the disc. I instead ignored the flak and focused on the disc. I also kept my corvettes nearby, strafing his disc's, in and out as I needed them too. I won of course, and only because of my eco at start.
Judging from this battle alone, I wonder what would have happened if Sinkillr had a larger flak fleet.
If Sinkillr had the same amount of planets at the start.
I do really think it might have worked, I'll have to try it out, but am very afraid to try it in a 5v5 game.