I'm a little confused by the standard argument here.
There aren't enough potential large ships in the Star Wars universe outside of Rebel/Imperial iterations?
Looking at Scum's roster in X-Wing gives you:
Mandalorian, Corellian, Black Sun Syndicate, Ex-republic etc etc. All very powerful agents in the Star Wars galaxy.
In fact Scum in Xwing tends to act as a dumping ground for everything not rebel/empire in the galaxy, rather than a tightly-defined set of pirates and traders. Why then would this be seen as a limited field of ships? I know they're not as iconic as ISDS, but they're certainly there in enough numbers to form a faction...
