well, a lot of us are alpha/beta players that have already planned a route to 60, with lots of stops on the way for gear farms. and because we already know where stuff drops and where to go to kill AND we already know the layout of the game / zones / mechanics--we have an amazing advantage over people that dont know any of those things and are experiencing the game for the first time.
classic everquest in 1999 was the same way. people that were in the alpha/beta were literally at level cap (level 20 when it released) within a few days. and were able to push to 50 without much trouble since they already had a very good understanding of the game / world / mechanics.
TTK is not the only factor in being able to level. its going to slow down A LOT for people that are having to compete at certain areas too. the benefit to leveling quickly out the gate is my (our) groups dont have any competition for zones, mobs, items, etc. every place we have gone to we are the only ones there.
the leveling will slow down immensely once you have to actually compete.