When compared to the other cap ships individually, I agree that the Marza's lvl6 ability seems very over powered. There's more to winning the game than capships though. When you stack up 500 fleet points worth of balanced fleets from each of the three races, the TEC will lose vs either of the other two most of the time. The basic TEC strategy is to out-produce your opponents since you will lose more ships then either other race. Even if a battle can be called a victory, the TEC still loses large numbers of ships, often equal to or greater than the number of ships lost by the "losing" fleet (unless they have crushing numerical superiority on their side). Taking this into account, the TEC can hold it's own with the other races when defending, but when their fleets move away from their frigate factories their ships are hemmoraged away rapidly making it difficult, and sometimes impossible, to mount any real offense.
That said, the TEC fleet needed some real hitting power that would allow them to be able to engage other comparably sized fleets offensively with a chance of having enough fleet left after the fight to linger in enemy territory and wait for reinforcements, capture planets, whatever the mission goal is. Otherwise: after each engagement, the fleet has to return to friendly space in order to be rebuilt before it can return to enemy space, by which time the enemies have rebuilt their fleet and it becomes an unbreakable standoff (at least until the other side decides to attack, then it's just a matter of time). That hitting power somes from the lvl6 abilities of the TEC's capitol ships.
Knowing this as the TEC means that (against an opponent familiar with TEC strategies) every one of those capships you build (especially Marzas, Dunovs and Kols) are huge bullseyes that will pretty much just draw fire and never see lvl6. I don't want to see a whole lot change though, because that would reduce the different flavors the different races have. The TEC are obviously the underdogs in this game, and every underdog needs a "Hail Mary" in their playbook, I think that the dunov's flux, missile barrage and finest hour are the hail mary plays for the TEC and need to be there.
If there's still too many people unhappy with the balance, and I had to change something; I would NOT reduce the TEC's abilities, but increase the # of ships affected or otherwise buff up the other race's caps. Honestly though, I like the balancing the way it is, it provides flavor to the different races and forces players to consider what their strategic tendencies are when selecting a race.
Wow, that got long-winded fast... Marzabating FTW