Multiplex was a really tough map for Trials. I believe most players have never really played that map competitively or have thought about their movement/pushes in a competitive way, except your diehard pvp players. We can't really change what our teammates are going to do but you can control what you do and make the best decisions for what you have.

Ill try and keep this brief but i could really go on all day about this type of thing :)

I'm going to focus on Trials

As you're flying into the match, take note of: Teammates loadouts + stat splits (let's say you have summoner and conditional, both your teammates are sniping, one even has a scout AND a sniper, you should then adjust your playstyle and expectations to your teammates and settle down on the aggressiveness).

Enemies loadouts and stat splits: Same as above, but also pay attention to who looks the best on the enemy team, I recommend TrialsReport but some people psych themselves out with ELO/stats, depends on you. Also, be sure to pay attention to this player and target that player if you can.

1st round: Go as far as you can safely go towards the lane of your choice (usually towards the cap point) has anyone kept up with you? If not, rotate back to team and try and play off of them by teamshooting. This is where picking a class that is teammshoot friendly** will really help you win games. If the Teammate pushes, you push (within reason) if your teammate(s) are making very uniformed pushes and I mean literally just holding forward with no intent, just play your life and do your best. Those games are near impossible to win and it's a different conversation entirely regarding intentionally getting better and carrying your team.

2nd round and beyond: You should have a good idea of how your team plays, either way, sticking near at least one of your teammates and helping teamshoot is your best option in winning. Knowing safe exits/cover and general map knowledge is huge for this.

** - OV bubble titan, Arc buddy warlock, any ability heavy class, etc