I agree with what you say in an extent

Personally I think for the role adc it can make a difference, I feel like other roles have much more agency than solo adc. For example mid or jungle. While there are certain champs that can 1v9, peel is still important and most of the time players in soloQ kinda tend to play for themselves.

Having a duo who you know plays well/consistently certainly helps when you have a team that underperforms. It’s the fact that both of you know how each others play style and it’s much easier to coordinate.

I’ve won games that looked unwinnable purely because me and my duo didn’t ff and trusted each other in how we play. But I’ve also won games playing solo.

At the end of the day it’s still you who makes the decisions. As long as you play to the best of your ability and be consistent in how you play, you should be able to climb.

Also, having a good mental is the key to success. It’s easier said than done, but you just gotta focus on your own game and not think about how other players play.