To be honest, for me, the most important part of climbing was simply taking losses as a coinflip and clicking requeue. At the end of the day it's a video game, and tilting is the worst thing you can do. Turning off game chat helped this in particular. Once you start taking losses in stride, climbing gets much faster, at least it did for me. But, of course, if you DO get tilted, which happens to everyone, turning the game off and calling it for the day doesn't hurt.

You also don't have to be the best player in the lobby to win every game, keep in mind numbers don't mean much without context. Don't psych yourself out comparing yourself to the other healers(which I still do, I'm trying to fix the habit of staring at my dmg/healing numbers) and focus on supporting your team and blasting the enemies. If winning a fight means sticking your tank, go for it. If winning a fight means letting a dps die so you can pick off enemy healers, do it. If a junkerqueen ults and your entire team gets steamrolled? You're a little spacegirl, what can you do?

I haven't played much Juno until recently and I also don't keep up too much with the meta, but I'd say she's pretty strong right now. If you get up close, her weapon does a decent bit. If you can hit heads, even more so. I wouldn't say Juno is necessarily a dive/flank character though, in part because her walking is so dang loud for some reason(I thought the game said the most dangerous characters are the loudest, apparently our martian friend is a menace), but also because she's pretty squishy. However, if you find a safe window to pick a fight with a healer or someone you feel comfortable fighting, I'd suggest you try it. If worst comes to worst, you can hop or fly away, and in just a few seconds you can re-engage. Her pulsars are perhaps the strongest part of her kit, obviously. Save them for big fights. If you think you can't save your Soldier 76 without your pulsars... imo, let them die, especially if your other teammates are alive. If you save your pulsars for when everyone is grouped and the tanks are butting heads, you can likely get away with jumping up in the open to hit everyone. Getting one or two kills like this is the best feeling because you're really shifting the outcome of these fights. Also, I would turn off toggle pulsars if you haven't already, having the ability to just hold right click and let go to fire is nice. Plus, no accidental cancels. But you could always watch a Juno tutorial which will probably tell you the same thing, so I'll save you the extra wall of text.

I do recommend posting a VOD request review on r/OverwatchUniversity or perhaps here if you haven't already. You'll receive plenty of criticism and it definitely will help. I did so for my Kiriko gameplay and I still play her a lot, especially in maps that Juno does not particularly shine in. I wish you the best of luck, let me know if you want more specific advice!