Well, Advent can match the others mostly in Heavy Cruisers though, from my experience (with upgrades and the Halycon aura and such Destras can be beastly), so I don't view them so much of a balance issue besides from how boring they can be (although that replay of yours rushing them in like 12 minutes then being called a cheater was a wonderfully fun watch).
But really by the time Heavy Cruisers are on the stage in significant numbers most games I've played or seen, there are support cruisers, which at least in the case of Vasari can mass-stun Heavy Cruisers, and Advent's Guardian can keep them out of range. Heavy Cruiser spam is nasty, but since there are more toys on the field, it doesn't seem as bad to me, at least.
Early game, there's really nothing but LRMs in order to win games. The Light Frigates are food for the LRMs, since LRMs are effectively their hard counter. Flak have been reduced in effectiveness against LRMs, though I'm pretty sure you can still use them, Flaks are so inflexible compared to LRMs; they can't kill Capitals, Structures, or Light Frigates the way LRMs can, making them tactically, but not strategically viable. Going Capital heavy is suicide because of how strong the LRM damage type and how poor low level caps fair in battle against a number of smaller ships (even Light Frigates). And Carriers, well, everyone knows their story, expensive, easily countered by units half the cost, high tier (later tier, except for Advent but what does it matter now).
I love all the units and special abilities and potential variety that is possible in this game. But how strategic can the game be I wonder if most of the battles are so tactically stagnant. Sure, you have a vast empire and the potential for massive fleets, but what does it matter when two different ships can get nearly any job done by themselves.
Also, ICO appears to be back up.