If you can control what map you’re playing on, you must split the elo brackets. You can’t reasonably compare the skill of 2100 islands player compared to a 2100 arena player. Without splitting the brackets, you can have absolutely no clue of the skill of any player, regardless of rating, on any map, because who knows what he played to get there.
This is a problem with the current system and it’s only getting worse the longer we have preferred maps and map bans, this is inevitable, and it needs to be changed.