I've been in this situation before, on a team with nice people who don't really care for improving and finding myself frustrated with the situation but not knowing what I could/should do. Like you, I began to feel extremely burnt out and disheartened, knowing I could be having so much more fun on a better team, not because I wanted to win but I wanted to improve.
You won't improve if you don't surround yourself with people who aren't necessarily better than yourself, just willing to better themselves.
I left my UGC Donut team for a team of similarly skilled players, only these guys were serious about strats and practice and all that. I'm not quite Prem yet, but I have a newfound enjoyment for the game and look forward to scrims and matches.
TL;DR, leave your team if you aren't happy with them.