Mailanka wrote:

What struck me was that nobody fought them.  At one point, I was invading the United Empire homeworld, and I could see they had 14 ships in their hangar, and I just sat there for a few turns, besieging the system, waiting for him to counter-attack, but he never did.  

You wouldn't happen to have a save would you? I'd very much like to probe this United Empire AI's brain...

Finally, a random aside: I've been trying the Vodyani and I'm still dissatisfied with brainwashing, as assimilation is better in all ways.  Why not borrow a page from the Cult of the Eternal End, and give Vodyani free mercenary ships from brainwashed system every X turns?

The assimilation system is going to be reworked, so don't get too hung up on how things currently work

Free mercenaries might be interesting, but the Vodyani are a very strange faction - we don't want to make them so different that they become effectively a whole other game