If the enemy fleet has about 100 ships, then...
TEC - will have enough Hoshis and HP/armor upgrades to negate 900 damage per target pretty easily
They lost all their shields anyway. Even if shields are only 30% of the TEC ship's durability, it is still something they'd rather HAVE than not. And they just lost it.
Advent - will completely shrug off this rather small amount of damage with a healty amount of Guardians and lvl 3 shield restore
That's a different story as Advent can pretty much tank MB right now.
Vasari - should have a lvl 5 Skinatra with repair cloud by this point, which will start the healing process. You're right in saying that Vasari have the short end of the stick when speaking about AoE healing abilities, however their ships are just so darn tough. Now, if your enemy is using mainly assailants, than he gets what he deserves. Enforcers have a huge amount of HP and armor, plus reintegration. Overseers can play cleanup.
Again, Vasari can't regenerate shields, which they obviously lost after even such a nerfed MB. Since shields are a little more important for Vasari than tec (relatively bigger shield-to-hull point ratio), this is again a serious blow.
And you can't assume one should have a lvl5 skirantra with any big fleet. Constructing a second most useless cap ship and leveling it to 5lvl solely to battle a marza is even more of a laugh than building a lvl1 most useless cap ship (marauder) to disable a channeling marza. Repair Cloud is no help in most big battles. Focus fire means ships blow up before the repair starts working.
My point is that, in large fleet engagements like you're talking about (and where a lvl 6 ability is needed to turn the tide of battle), merely hurting a lot of ships isn't good enough. You either need to cripple the enemy in a particular way (disable key capital ship, disable support cruisers, etc), or kill a lot of ships quickly.
If all the ships start dying 30% faster because they've just lost 30% health (shields)... I'd say they are crippled.
Advent is a different story cause they ignore almost all AOE in the game.
Vol nanites? One of the ships blew up? 150 shields lost, that's 3 seconds of regeneration. Lul.
Malice? Same story.
Rad bomb, PMS... same story.
So for TEC and Vasari, hurting a lot of ships IS good enough. For advent... they can tank MB as it is.