Since a recent update, story quests were given much more XP, and zone quests XP rewards were dramatically reduced. As of that update, it was easily possible to level a character from 1 > 65 using only Story quests. I’ve done that many times with all except Sorcerer and Archer.
More recently I found that it is easier to level any class from 60 > 65 using almost only dungeons. In this pattern, the story quest chain is stopped after doing the quests in Highwatch.
I just completed leveling a Mystic character from 22 to 60 using only dungeons. Starting with Bastion of Lok at level 20, and completing in the Ebon Tower reaching level 60 after two runs. You can find a list of all the dungeons here.
There are a few Caveats with this method of leveling.