How do I get better at this game?

I have been trying my absolute hardest. I try to counter swap, strategies. For the full context. I play dps. I started playing near the end of last season and got to gold 1 only playing Vendetta and Genji. Then this season I've been playing Vendetta, Tracer and Anran. Ive been mostly playing Tracer and Anran since vendetta gets banned a lot and I managed to solo que climb to platinum 2 almost 1. Ive been on a consistent chain of loss streaks down to demotion protection on plat 5 almost gold 1 again.

Here's my experience. There are games we're no matter what I do im getting farmed and our team is getting obliterated. Or games where im popping off my tank is getting diffed too hard. So if I have a good game, ill lose and if I have a bad game ill super lose. It feels so difficult to climb and I sont feel like im actually improving. When I win it feels like the enemy team is just bad. How do I get better?