Though they have removed the ability long ago to que in large groups, 5 people can still que up together. However, premade groups (who organize on discord servers) have since figured out ways around this limitation. When accused, they will actively gaslight you into thinking these groups don't exist, claiming it's "impossible" since they nerfed the size of party quing. However, being apart of numerous major PvP discords, I can confirm Frontline premades are very much a thing, and are very much damaging the Frontline experience for the solo player,
So how this works is that multiple groups of 5 will que together at once. They will all be in a discord call in order to coordinate. They will randomly get put into any of the 3 teams, some on the same, some on opposing teams. The winning side is determined by which team randomly got the majority of the premade. The ones who aren't on this side will then actively throw the match for the determined winning team. Due to the RNG of matchmaking, this doesn't always work out and this won't work, but it still often does.
So let's say 25 people que up in 5 split groups. 15 of them end up on Blue, 10 of them end up on Red. Blue is the determined winner since the majority of the discord ended up here. Have you ever noticed the other two opposing teams will sometimes ignore your team as well as objectives and fight eachother, then suddenly pinch you will level 5 Battle Highs and farm you to death while one side ends up taking everything and winning? Well that's a part of the strategy: The two colluding teams will fight eachother, ignoring the third team as well as any objectives that aren't in their immediate vicinity. They farm eachother till both of them have high level battle highs.
After which, the one team with less premade players will focus on stifling the third team (directing the pugs on their team into focusing down the third team), meanwhile the determined winner team will actively cap all the nodes, without either side inhibiting them. The third team cannot stand much of a chance because since both sides were ignoring them until they got battle high, they couldn't have gotten battle high themselves are now being focused down by 24 level 5 Battle High players who are heavily coordinated.
While it is possible to counter and defeat these premades (I have myself a number of times) it's extremely unlikely as you are facing 2 teams that are actively coordinated against you and abusing the Battle High mechanic to their advantage. If you see the behavior I described in Frontline, you are almost certainly up against a coordinated discord group.
The solution I think would be to remove Battle High altogether. I don't know what else could be done because multiple groups queing at once are almost guaranteed to end up in the same match, but Battle High is very important to their strategy and the removal of it would pretty much stop them. When two teams are able to coordinate, they can kill eachother to get battle highs and share points, then the third team has basically no chance against either of them. Personally I would actively go through these Discord servers and mass-ban everyone involved permanently but I doubt SE would ever go that far sadly.