Level Progression/Questing

[Zumi]

#3 is not really an option if it is not efficient, which is potentially the problem. Having the option to do something but it being completely pointless is not really an option at all. Just like in WoW you can level up only killing mobs never questing or running a dungeon... but it would be stupid.

Sounds like you haven't played WoW currently. Actually grinding mobs in WoW is the fastest way to level in WoW. Just that nobody does it because it takes a group and a vast amount of knowledge about monster spawns around the world. All the world first level 80, 85, 90, or even server firsts are obtained by grinding mobs.

For example in the newest expansion MoP someone went from 85-90 in 5 hours, many server first level 90s were done on grinding mobs, questing takes like 1-2 weeks on average for your normal person. Only extreme hardcore people grinded mobs cause its really mind numbing and takes some coordination to have a group together. People will go to spots where higher level mobs spawn 89-90.

In cataclysm the guy who got the world first 80-85 did it by grinding mobs that respawned fast in Twilight Highlands.

The main factor is most casual players in WoW will not grind mobs because its easier just to quest solo or dungeon queue then find a group of people your level to grind mobs even though its the fastest way to level. People would rather spend 2 weeks getting from 85-90 rather then 1, 10 hour exp mob grind session, which really only the super hardcore do.