Unfortunately it isn't just premades, because I've seen a premade (DRK/AST/AST/AST) with at least two other ASTs in tow, getting just as much kill participation. I don't know how it could be done with the way the game is designed, but there needs to be some degree of restriction on how many of a job is in each alliance. Either that or nerf AoE damage to make AST less of a nuclear bomb when stacked up with so many of them.
I honestly wouldn't mind if my first suggestion made queue times longer for FL, because then I'd get into a match with a chance of winning. Right now it's 100% loss rate if these DRK/ASTx3+ groups are in the match. There's no competition if one team is guaranteed to win every time.
Also, today after seeing the same group again I decided to send one a tell since they're on the same world as me. It went about as well as you'd expect, since they don't care about ruining the game for other people:
It really shows that they believe they're entitled to the win more than anyone else, which actively disrupts the gameplay for most people in those matches.