RR has very little translation from other schemes.
Whilst the others have many things in common, if you master all schemes except elite or intermediate, it will take you only a couple of games to become competitive at them. Doesn't happen in RR no matter how good of a roper you are.
The skill in elite is not really imposed by the scheme but your opponent, is more of a mind battle so it'd be hard to theorycraft about maximun skill limits.
Bng is definetly not the hardest. Provided inhuman practice I'm pretty sure a couple of players currently playing could achieve something close to a game were they hit every turn for +40 damage, which is not perfect, but it's much closer than comparing Mablak (or whoever is good at RR nowdays) to a tool assisted replay in a RR.