Since we got a similar line of discussion over in 6E+ thread, I think nailing the right formula for the zero to hero is the trick. 5E, for instance, has pretty low key and vulnerable levels 1 and 2. This is so folks can have that surviving by the skin of their teeth and becoming a capable hero thing. For some thats just the right amount because they can go by quickly as a campaign sets up. For others, its a pain becasue they dont want to experience those levels everytime they start a new campaign (but many players and GMs only want to start at level 1!). At the other end of the leveling spectrum, is the gonzo fantasy. God like spells, fighters surviving orbit reentry falls to the planet, etc.. Some folks want to play that, and they dont want to wait until level 10+ since, as mentioned folks want to start at the beginning and most games dont make it past 10 so may never actually get there anyways.
Im not sure the best formula though i think its less levels, to the chagrin of folks who want 30 level D&D, I just dont ever see that in the cards anymore in face of the amount of folks that barely get past 10.