someone who is super strong on Arabia should be also usable on Black Forest
Similarly, islands, whoever can do Archer Micro won't go down completely.
If you consider them completely separately, you also run the risk that a player has too few games on individual ladders for decisive ratings.
it's like `core rating + open rating` and both have to adjust a bit after one game.
or `core rating + open rating + 1v1 Rating` e.g. and then you can even weight them
something like core rating counts 50% of the overall rating, open rating 20%, 1v1 rating 30%
`core rating` can be also including the starting rating from another ladder/from another rating system with a factor to include it into the core rating for migrating from other platforms (something like this is existing already on ncZone)