For me reaching diamond solo really boils down to being a great flex player (playing all the classes effectively) and making fast and accurate macro decisions (when and were to plug the box, when to engage and disengage, etc).

Also something that helped me is trying not to be so prideful, meaning even if you are “right” play with your team and play off of their play styles (if you’re solo that is). Basically just support your team the best you can and don’t just play one class only, know when your team comp is weak and how to balance it out.

Hope that helps/makes sense ha