I tried the level 6 Marza for myself the first time yesterday.
I have to say Missile Barrage is SO far and beyond better than ANY other level 6 ability in the game it definitely needs balancing. A number of targets cap seems appropriate. I mean.. how many missiles can there possibly be??
The fact that you can interrupt Missile Barrage with a select few other cap abilities doesn't make it any more justified. You can interrupt Cleansing Brilliance, Provoke Hysteria, Drain Planet etc. etc. as well. But none of the other level 6 abilities vaporize entire fleets of ships in a huge radius to begin with.
Missile Barrage needs to be balanced to be in line with other level 6 abilities.