Advent's shields granted from hangar defense don't stack. Already checked. It gives ~750 shields where none existed (actually on second thought that might have been with shield bonuses researched), and thereby shield mitigation, which is obviously the primary point, but the shields don't stack.
Vasari hangar defense is arguably the best, IMO, as it can disable enemy strikecraft for ~45 seconds at a time.
I haven't experimented sufficiently with TEC's hangar flak upgrades to determine how worthwhile they are.
TEC do get two abilities for their turrets.
-
I think you may be missing the point.
My original assumption based on looking at the ability was that it was overpowered. Now that I have tested the ability, I see that it is perhaps slightly underpowered (only slightly because if you want it that badly you have 35 tactical slots that you can spam up with 35 missile platforms), where the logical solution, that of having it affect all targets in range, would make it massively overpowered.
I don't understand how making it have a maximum number of targets in range and giving it a cooldown would make it worse. It would in fact make it better under the circumstances where you don't spam the platforms. Right now it's just going to shut down the regen of the one ship it's firing at until that ship is dead.
Considering that in my testing the duration is ~5s, at present spam is the only way for it to really help. It is possible though unlikely that something is interfering with the duration (perhaps damage) and that it is in fact a 300 second duration, as displayed. If so, I'm confused.