They have, if memory serves, an 800 default soldiering. You're not invading, PERIOD, until you pick up tech for adv troop modules, minimum, even if you don't need the adv modules themselves. You'll get SQUASHED.
(Which makes it funny when they show up a month into the game, but that's another story altogether.)
Again, if you give them time, or if this happens to be on a gigantic map where you don't control everything yet and they're in a distant system, they can actually become a challenge.
I do agree that when they show up due to Mega Events they're weaklings, though. But then again, I think we all do.