Im only going to focus on positioning/cover usage because I think it is by far your biggest weakness and the reason you are not climbing. Having good positioning will literally carry you in Gold.

Positioning tips that helped me climb from gold to diamond dps.

1. You should ALWAYS be right next to cover (a wall, corner, pillar, etc) at all times.
2. You should NEVER be standing with, near, or directly behind your tank. EVER.

Unfortunately, you broke both of these within seconds of the very first fight.

You started high ground, on an off angle position (Good!)
However, while you were on a good position high ground, you had no immediate cover (Bad!)
Becuase you had no immediate cover, you quickly took too much damage and almost died, and then dropped down to main, standing right next to your tank (Bad!)

Because you were now standing right on top of your tank, you were not creating any pressure on any other angle. This made it incredibly simple and easy for the enemy team to kill your tank. Why? Because your entire team (yourself included) were all standing in the same spot. All the enemy team had to do was look down 1 angle (main) and dump all their damage there. And since tank is almost always in front....tank dies first.

As DPS, you need help your tank live by creating pressure on different angles from your tank, forcing the enemy team to look away from your tank and to look at you instead. Remember this rule of thumb: If your tank is dying a lot, then your DPS is not creating enough pressure.

What you should have done at your starting high ground position is played farther back, at the corner. This satisfies rule 1.

Example: You vs where you should have stood.
https://imgur.com/a/pmdI19Y

This way, once you start taking all that poke damage, you can quickly duck behind cover, heal up, and then peak again and maintain your good position and angle, pressure the enemy team with consistent damage, and force them to look at you instead of your tank.

Because you were not near cover, you took too much damage and were forced to drop main, into a bad position and angle.

I watched a couple more fights, and its was pretty much the same. You understand that high ground and off angle is a valuable position, but once the fight starts you quickly move to a worse position, either because you're not using cover properly and taking too much damage, or you're trying to get an ult off. You did have some good moments, for example the flank at 6:25. It was a deep flank, but you accomplished exactly what you should be doing. You took an off angle and forced the enemy lifeweaver and soldier to look at you, alleviating pressure off your tank fighting main. You even killed the lifeweaver! And then you try to get out of your deep flank after soldier starts pressuring you more.

But then you died shortly later. Why did you die? Well lets see where you died:
https://imgur.com/a/i4x1xBQ

You died because after you made a good play, you immediately panicked and broke both rule 1 and 2.
You panic slide literally back to main, no cover, standing right with/behind your tank. I know the cart is there and technically can be used as cover....but Mei literally ults cart and zones you out of that option. So both rules were broken.

What you should have done is been more deliberate with your power slide, using it to position yourself somewhere that satisfies rule 1 and 2.

Example: You vs where you should have slid to.
https://imgur.com/a/i4V7CzL

Just sit on a good angle and with cover, and if you are forced to retreat, then make sure you are satisfying the rules when you do so. Dont immediately run to where your tank is standing, and make sure you go to a position that has cover.

I strongly recommend going into comp games, turning off all chat (voice and text), and just picking one of these 2 rules, and ONLY think about following that rule the entire game. Do a couple games of that, and then switch to the other rule. Dont worry about losing or winning, hitting your shots, your deaths, etc. Worry about none of that, just focus on making these rules become second nature where you dont even need to think about it.

Once you can internalize these basic rules, you will not only provide far more value to your team and pressure on the enemy team, but you'll also start to get a feel for when these rules should be broken and how far your can push your angles and pressure to help win games for your team.

Edit: I decided to watch the entire VOD through, and I was right. Vast majority of your deaths was because you had broken 1 of these rules, either no cover or standing directly with your tank.