You forgot adding "for me", as these are not facts, but just your (narrow) opinion.
On leveling a character you can make a lot of decisions about what quests area to do and skip, which keeps plenty of room for alts to experience some unexplored path.
Moreover and more importantly a very big chunk of your leveling experience is your class quests and they are different for all characters to enjoy.
I also find that just playing as different character, which different abilities and motivations keeps the experience fresh.
If that all doesn't work for you then just move on - This Is Not The Game You're Looking For.
And it doesn't have to be. The game is what it is, and there's no need for everyone to like it. I am not sure myself if I will still be subscribing in 6 month's time, think about that after this short time in-game is stupid and childish - just experience the game until it's not fun anymore and then play something else.