Bigger issue than people making small parties in Frontlines is the lousy current balance.
People wanted to tune down the AoE spam, because their only tactic was deathballing and still is.
Now since everyone was given unholy amount of damage resistance people use what still works.
Your best bet is to wait for 7.0 Frontline revamp, I doubt they are going to make larger changes until then.

As for partying up in general, I would love to see them allowing it in Casual CC. If people are worried about it being valuable enough for higher rank premades coming in and stomping, then increase the Ranked rewards in comparison so much that it's not worth it to do over just playing Ranked.