Each capital ship unlocks a special power at level 6, this is normal.
But, the TEC union Marza Dreadnought capital ship's Missile Barrage power is overwhelmingly powerful. It hits everything in a radius around the ship for approximately 2,500 damage over 5-10 seconds. This is enough to wipe out any non-capital ship and severely damage buildings as well.
Additionally, the tendency for enemy ships to clump together means that you can fly a Marza Dreadnought into the midst of a pile of ships and wipe them out in a single shot. Every ship in the area of effect takes the damage, so it's not hard to obliterate 20-30 ships with a well-placed attack. This is particularly effective against pirates!
Other players who know what they're doing can reduce the damage of this attack by moving their ships away from the Marza Dreadnought. Or, with the right attack options, the Missile Barrage can be interrupted/countered.
So, while not unstoppably deadly, the TEC Union's Marza Dreadnought is head & shoulders above its peers and something that players need to stay on the alert for.