I think that the XP should be a bit lower than in the Korean (final) version. Western gaming culture is different, and people here don’t like grinding as much as the Koreans do.
Personally, I wouldn’t mind the current system (in fact I’d prefer it), but I want the game to be successful on a large scale, and for that it has to appeal to casual players who want to be able to experience progression on their characters on a limited time budget.
Not everyone is a hardcore gamer and has a lot of time on his/her hands. The final levels will be extremely hardcore anyway, because of the exponential XP scaling.