No matter what the exp curve is, there will be bitching. Lots of it. If it's too slow, people who validate themselves through the game will feel less special - if it's too slow, the game will simply lose memberships entirely from people without the time or motivation to grind that far because when they get there it [I]won't[/] make them feel special.

How long gratification should be delayed for maximum effect will be different for everyone.

That said, I much prefer the "Western" trend of easily making it to endgame and then grinding endgame for a long time while having a complicated system of "fleshing it out" in other directions than I am the "Eastern" style of having the grind be the path up to simple, repetitive endgame grind.. (Both opposed to the Korean style of both?)