http://tvtropes.org/pmwiki/pmwiki.php/Main/FactionCalculus

General theory on development of factions as a game progresses.

So, according to this theory, it appears that Rebels were a "Powerhouse" faction (i.e. Falcon, low-number ship builds) and Empire was a "Subversive" faction (i.e. Swarms, mini-Swarms).

Now, we have Scum and Villainy, who will probably be the new "Subversive" faction and rely on tricks (e.g. illicit upgrade cards, unusual abilities). Empire will be in comparison be seen as more "Balanced." (because you could play Empire with one big ship (e.g. Decimator) and a small one (Squint? Bomber?). The most high-costed Scum and Villainy ship seems to be no more than 30-40 points.