Failing to address multiplayer in PVP is a mistake

[Valence]

First timers are going to start in casual. If they keep getting curb stomped by premades then they will give up on the mode. I would personally prefer casual to be welcoming to newcomers.
The only way this would work is if both teams had a premade on them, or neither had one.

They will not be curbstomped by duos more than how they already get curbstomped by solo ranked players anyway. And at the opposite of solo ranked players where you'll never be sure that the other team also has one to even the odds, a system of duos would required the other side to get one too.