Even games that are considered average like Warhammer Online or Age of Conan offer very compelling story-based experiences at low level, with a lot more density than FFXIV does.
It is good that you mention those games, as everyone I know has said that the first 20 levels of AoC were brilliant while the rest was horrible. A classic case of putting all your attention to hook people and not thinking about how to keep them hooked as well. It's not the first 20 levels that matter, it's the whole package. And if the whole package is solid, people will keep going. AoC didn't have to make the tutorial as good as it was, they could have easily balanced it out with the rest of the game and people would have liked it a lot more.

What you say and what your examples are do not go hand-in-hand. To AoC, to WAR, to Aion, increasing density in the lower levels did mean neglecting the higher levels. What you are proposing here is the same thing. "Put most quests in the lower levels, ignore the higher levels for the most part." If that isn't decreasing density, I don't know what is.

I edited my post above.