Not sure if I fit but I've peaked around 1600-1650 elo on ladder so I can attempt to help
Teambuilding doesn't matter if you can't play the game well, and the best way to get out of this is to use pre-existing teams.
Very simple team, get rain, keep rain, use it to sweep. Hurricane has 100% accuracy in rain, and Fire attacks are weakened, making Magearna a fearsome late game sweeper. Try to make sure Pelipper doesn't die, and yeah.
This type of team generally features defensive pokemon that you can switch into so your threats don't die. Then, while everything gets chipped, your fast, hard hitting thing comes in and wins. Or your other thing gets stats from setup moves and wins the game that way.
For the most part, don't change the teams yet, get to know the game a bit better, then you can try to make your own team. PM me if you ever need advice