I put this together last night.Defeated their portal with only two 20k fleets, mid-game auto-designed ships. Purely tactical, brain over brawn is one satisfying way to deal with OP AI fleets.Newer versions of Stellaris though will require roughly the same tactic, but multiplied by the number of portals they will be able to build. It's hair-raising, but if you time everything right, it's a beautiful thing.I did forget to mention though that this tactic also relies on a little bit of luck in hoping that the Unbidden don't magically spawn another 50k fleet right in the middle of the portal you are attacking. But then again, it wouldn't be a risky maneover to attack it with only a 40k fleet otherwise would it?Good luck!