Umm... it only takes 8 or 9 hours to go from level 1 to level 70 at a casual pace right now. Yes, it would take longer without league of levelers, but certainly not weeks, let alone months.
Now on one hand, I don't think it's unreasonable to expect players to level at least one character normally before allowing them to instantly level characters.
On the other hand, you don't actually learn to play the game while leveling anymore. There are still an abundance of people who level up normally and still fall in the "I don't know what I'm doing" category. So would it really make a difference?
Im not sure how long the gameplay is, however you must consider that:
1: most casual gamers can only spend 1-3 hours a day on games due to work, family and other needs
2: side quests are a thing that people do take as a form of completists
3: I dont want to waste that much time to regrind the same missions and running around (especially the citadel of torment, confusing as hell)
I can understand wanting a restriction of "you must complete the game without this" in order to obtain it, however, not everyone is interested in continuing the story or wanting the best gears. People like me just want to be at the high enough level to enjoy the rest of what the game offers: Crafting, fishing, possible roleplaying and even helping new players.