You are doing it wrong.

When I'm playing and all team members have a store of 700-800 it usually means that team wins.

Same here. I'm always the top player in points out of both winning and losing no matter what. The reason this happens is because people just want to shoot each other. They don't understand or care about winning.

If he's getting 1,500 like he says... he's not the problem.

You could rename this into "Why do I get such noob teammates in X, lost Y times in a row"

Maybe he sghould start getting 2000 and more then to carry his team?

I have no idea what points in Splatoon mean. I only know that in RL they mean shit and noobs still use them to justify how "good" they are.

It's annoying, but I'm generally the top player in a loss, so at least I'm satisfied that I did my best.

The real pain in the ass is playing a match 1 or 2 players down.

Having a lot of shots on goal means nothing if they never equate to an actual goal but they still net you points... this is basically the same thing. You can get a lot of points for painting the ground in Splatoon but if you never kill the other team they are just gonna paint right back over it. Thats why somebody with 800 points who also gets kills is more useful than that guy who scored 1200 points and got no kills.

Dont blame your team, take responsibility

I perma removed Rocket League from my Steam yesterday, it was very bad for my mental health. The last game was the last straw - my teammates kicked the ball in our goalkeep in the first seconds of the game after passing to each other. I didn't care cos I saw stupid shit all the time, but they kept doing stupid things all game and I got madder and madder until said enough of this shit and googled how to remove games from Steam. I am free now, I play only games that give me positive emotions, well not really =P

Perhaps you should just give up on team multiplayer games and only play 1v1 type games then you only have yourself to blame.