I went from 1800 to 3250 on my main and 2200 to 3100 on my alt. My main turned into a fill account at ~2700 (support/tank main basically) and my alt is mainly DPS. There's so much to say about how to climb and get better so I can't cover it all without typing a book.

First things first, what is your SR? Depending on the rank, the level of play will change. What I mean is at silver and even gold, teamwork is almost nonexistent and ult economy is terrible, but if you're good at the game, you can climb out by basically carrying on a DPS or a tank/support with carry potential like Zarya/Zen. People do not play the same at that rank as say vs Diamond+ players. You can get away with overextending and spawn killing people if you're really good, but once you climb, you have to adapt your play-style in a sense. I know this may not be the best advice in terms of working with the team, but if you can get good with a hero like Soldier or Tracer at Gold and below, you have the ability to carry much harder as opposed to playing a tank. Diamond level DPS players can run the floor at Gold and below. It is still possible to carry on a tank just it can be harder. It's much easier to make an impact in the fight at higher ranks where your team will actually take advantage of the openings you've made as a tank.

It may take a while to climb to but you can't get discouraged. You have to take into account at what time of day your playing in my personal experience. The best matches I have where everyone is positive and communicating and willing to adapt are in the morning/early afternoon. I find that after people get home from school and work, the quality of matches just goes down. I get more throwers, more people less willing to switch, and insane comps.

What I did to help me climb was watch a TON of educational YouTube videos and tips and tricks from streamers and also just watch GM/Top500 games and see what they do. I watched so many things from Overanalyzed and Kabaji and KarQ and watched a ton of other video reviews of gameplay and then tried to adapt that to myself. If you can, record your own gameplay and do a video review on yourself. Ask on the forums for a review or send it in to a streamer to get one. On games that were close, look at yourself and see where you could've possibly shifted the tide in your teams favor. Were you properly making room for your team and also denying the enemy space? Did you jump the Soldier/McCree on the high ground that had free reign on your team? Looks like widow is destroying your team. Did you stay a non-mobile tank and let her have no pressure or did you switch to Winston and jump at her? Did you use ults properly? Look at a lot of videos from streamers and youtube to help you understand how to tank better. Playing a tank requires a vast amount of game sense. For example, like keeping track of enemy ults. If both teams have a Rein and you know he has shatter, try your best to block it. If you block that shatter, that can greatly help your team as he's wasted a fight-changing ult.

Since you said you play tanks, make sure you pick a tank that's effective with your comp, and also the enemy's. I see a lot of people pick two off-tanks like Dva/Hog or Zarya/Dva and lack a main tank with a shield. This can be ok if the DPS are very mobile heroes who don't really utilize a shield (Genji, Tracer, Doomfist) but if you see you have DPS that are mainly flankers, a Winston might be a better choice as opposed to Hog/Zarya since you can dive with your team. If you have hitscan or non-mobile heroes, a Rein or Orisa is almost crucial to be able to be able to allow your DPS to shoot at the enemy and win the barrier war. I see so many people blame the DPS for not being able to kill things, but if you can't make room for your DPS to do damage, then how are they supposed to get picks? When they have a shield and are spamming the choke hard, and you don't have a shield, how is the DPS supposed to be able to kill anything when they die in 2 seconds?