It's impossible to climb

I am a Lucio one trick and I've been high diamond-low masters for a few seasons I even managed to climb to masters on an alt and yet after the nier collab I went on a losing streak to plat1-diamond5 and I've been stuck since.

You would think this means easy games or at least that's what I thought and sure I'll get a game where the enemy team is just absolutely incompetent, but most of the time this isn't the case and it is the most miserable experience and feels almost impossible.

I feel like I am doing what I need to do I'm booping ball or dva away when they try to engage while trying to peel for my support and healing, but there is only so much I can do and sometimes I lose track of the ashe and amongst the chaos I get 1 tapped meanwhile mercy players (respectuflly) do fucking nothing 0-8 stats with 10k+ heals they just sit in a corner twiddling their thumbs. I'm at a point where I'm considering getting coached just to see what exactly I'm doing wrong, but I feel like I build ult fast I manage cooldowns well I try my best to hold positions and apply pressure I know I'm not perfect, but i don't think there is a reason I should be struggling.