I don't get the whole "new player" arguement people are throwing around either. If anyone should be able to enjoy leveling, it should be new players because the game is exciting and, wel... new to them.
In classic it took me a ton more played time to level my first character from 1-60 than it takes me to get from 1-90 now, and yet I enjoyed spending all that time leveling more than I do now because it was something I never did before.
Just because people that have been playing for ages have seen the leveling content that WoW has to offer so many times they are getting sick of it, doesn't mean new players won't be able to enjoy it.
Don't get me wrong, I wouldn't mind if they speed up 85-90 a little for players that have a max level character already. Why there weren't any heirlooms that scale up to level 90 in this expansion in the first place, is beyond me.
Leveling was challenging to you back then because you hadn't done it before (and game mechanics and itemisations were bad and half the specs in game were horrible). Now you know how to play the game, you know how to play your class blindly, and you have seen the leveling content before, of course it is less challenging to level in that case.
Also, fun is kind of subjective. While it isn't fun to you, it can be to others.
WoW is not struggling to get new players thanks to the game design, but because it's an MMO that has been out for over 8 years. It's quite a feat that they have managed to keep such a huge playerbase over the years. People these days will look at it and think "hmmm, I'll go with <insert 2013 game title here> it looks much more pretty".
I'm sorry to say this, but your post doesn't makes little sense.