DC space civilizations tend to be on the smallish side- one main world, maybe some others with other species under their control. I don't think any of them has much more than a dozen. The big wars tend to be alliances of many of these civilizations.
You've got 100 million battle droids and 100 jedi.Jedi are much smarter and much more powerful but as i've always said there is a certain point which at no matter how strong you are you just just overwhelmed by sheer numbers.
__________________ Some men, just want to watch the world burn.
I gotta admit, when Thanagarians show up, they're generally reasonably competent. A bunch of winged guards are often something to worry about, and during the Rann/Thanagar war they did stuff like try and cut Rann off from it's allies.
Skrulls have some smart people, but their average trooper is pretty dumb.
Skrulls were crippled by PIS. Even so, the way they actually figured out how to get arround earth's detections and several other science and tactical feats for that war were very impressive for them.
The empire at its peak would annihilate Tannagar. It was just too big and powerfull.
The only really big space empires I can think of in DC are Starro's Empire, which covers galaxies, and recently the Citizenry from Wonder Woman, who are space nomads with 200,000 ships, each of which individually is a threat to planets and have tech stolen from others over millenia (including a lesser version of GL tech for their blasters and shields!).
Intelligensia (super computer of countless minds - copy of Kree Supreme Intelligence), starships with warp capability, access to magic, K-class mutant gene in the Deviant Skrull race, created the Cosmic Cube, possess Cosmos radar that can scan as far as Earth & see Captain Marvel from the Skrull throneworld in the Andromeda galaxy, & the ability to steal/copy powers of other beings & grant it to their Super-Skrull/Warskrull super soldiers.
P.S. rule a 1000 worlds in the Andromeda Galaxy (which should be more like million worlds since they dominate a galaxy with twice as many worlds as Milky Way - leftover number from 1970s), and have ruled empire for a million years.