You guys aren't being realistic. People don't want to feel stagnant. If they put in an 8 hour play session, they want to see progress, advancement, and gain power. You can't just say, "the gameplay is good, so who cares how long it takes to level" unless you want people to burn out.
I think Vanilla WoW, if you remove all other factors outside of time-to-level progression, did it the best of any MMO ever. Again, just purely speaking from the perspective of time put in, to levels go out. The fact that they did an always visible, screen-wide exp bar helped as well. Every kill, you saw that bitch move.