Only one of Superman's Cousin Kara is allowed to have a personality at a time, and most writers give it to Power Girl instead of Supergirl. Peej, being firmly an adult in all versions, seems a lot easier for comic writers to get a handle on than the maybe-teen Supergirl.

Here's the thing: drone striking your own citizens looks bad on TV. Executing your citizens in the street looks bad. Military morale cannot survive a civil war scenario, especially when we have decades of proof that guerilla warfare can break them.