Well, it doesn't really do anything productive per-say, except maybe begging for kills when one team is guaranteed to lose regardless, which helps toward the kill count reward.

At the same time, I've never seen any insults. Thou considering that me and my mate are pretty nice people, we won't be insulting others. And we are using our own team instead of copy paste metas and, being ftp, we aren't using any of them "event ninja" probably curbs any hostility toward us. After all, even if someone with much less power is matched against us, they won't be blaming us for "having too much power" but rather the fact that matchmaking is poor. So we don't get insulted as a result.

Thou I am curious about what "speciifc lineup" you are talking about. The most hated on lineup rn is water healer team, which does not work nearly as well in 2v2 compared to 1v1--because you can actually focus down a healer using all the damage of 2 players, which pretty much destroys the build. And if 2 people focusing on one ninja can't kill it.... well, you aren't going to win even if they were using some other team so there is no point in complaining. (alternatively, you could hard cc both healers of one of the team) So there aren't really any non-event-ninja lineup that are super pesky afaik.