Yeah, these are all most of the reasons I don't like to play Gambit. If I'm on a 4 stack and we can cut up while we're playing, I'm fine. Otherwise, it's usually someone trying to complete a bounty, triumph or something, then they leave or they just don't try.
I'm fine with people not trying when it comes to the crucible and 6v6. But the 3v3, and they leave mid-match. erg!!!
Gambit games are horrible now. I've played games where my blueberries lose more motes than they bank. The other team beats the primeval before we even have ours up.
So, I just write off the triumphs for Gambit. It's not worth me playing a game mode I just don't care about. I'd rather be frustrated in the crucible.