What rank difference lets you win on random champions?

So most of us know how important champion mastery is. We're constantly told to pick 2-3 champions to spam nonstop and don't play anything else but I've noticed that higher elo players seem to dominate on most champions that work with their lane and even a mass of champions outside of their lane. Maybe these players struggle more when faced against people in the same elo but if they play with friends they dominate regardless and even against their own elo they seem to be pretty proficient with most champs that fit their lane. Alois for example has a guide on just about every top laner.

I've got a friend who previously peaked diamond 1 and when he plays off role or on champions that he almost never touches he is still able to carry in silver - gold. Obviously diamond is levels above so it makes sense but a gold player on a champ they permanently play Vs a diamond player on a champ they don't touch off role and still losing us a bit rough.

So I'm curious that if there was a graph that showed what rank you'd need to face to be order to win on random champions or in off role positions what would it look like?

I'd say same role but unfamiliar champion is easier than going off role for a start.