Regarding the superweapon thing... why not limit it to one but allow it to move with a cooldown, e.g. every 20 min to another planet. That would a) get rid of those shots taking an eternity to reach their destiny and

allow persons to get rid of them. They might need a buff though if they are limited to only one (not really sure about it).
Can anyone explain how Illuminators could not be considered overpowered? They have a different damage type and fill a different fundamental role from their TEC and Vasari counterparts, with a form of damage that no unit, even capitals, is strong against.
I'm not claiming that they definitively are overpowered, I just haven't played enough games yet to be sure. But beyond the basic stuff like PJI, Illuminators seem to stick out as being pretty definitively superior to what the other two races can put into play.
I would say they are different, not overpowered. Looking at the base stats they have shorter range than the other LR Frigates until fully upgraded. I mostly play Advent so I am not too familiar with the others, but the Vasari counterpiece can be freaking annoying aswell when fully upgraded and in a good setup so it get's the extra shield avoidance bonus.
Regarding the siege frigates... I actually don't have too much of a problem with them. They are annoying in the first and beginning of the second half of the game, but in the end they are pretty easy to deal with in my opinion ^^. It just takes a bit of time to find the right counter for them in each race.
Edit: The thing that needs the most fixing is the culture in my opinion. At the moment it is only good for prohibiting people to settle on your planets after they wiped out all the population which is ... nonsense to say the least. Seeing how long it takes to neutralize and enemy planet with culture is not quite fitting in a context with what it is supposed to do in my opinion. A good change would be for it to start influencing the enemies planet slowly but than speed up at an exponential rate (snowball system so to speak). Also it takes way too long on your own planets to spread your culture in my opinion.