I've never understood why you don't have PvP locations in every world. This could be implemented in both Wiz and Pirate and could alleviate a lot of your level gap problems in the current format. For wiz I would think having 10 and below in Wiz City, 20 and below in Krok, 30 and below in MB etc etc. That way people can fight as high a level as they want in ranked pvp, but can also cap it based on their own level.
As to P101 even though there is only a practice arena by putting them in each world you get much more balanced matches for those that want them. There will still be bottom feeders hanging around Skull Island to take advantage of younglings, but the core people looking for players more their level and not wanting to fight the low levels that jump in random matches would be able to do so. Right now even with switching realms its a juggling act to prevent people jumping matches. Since the world is new a low level really needs to make an effort to get to Mooshu.