Loot pool logic is something that developers can easily "fix". The first though that comes to mind as just an example is giving guaranteed chest upon defeat of the boss that will give one piece of gear for whatever class you open it as. Something like the chests with Red Mage and Samurai gears, except only one piece and based on the current class, not for a fixed one.
After that, add one drop that is randomly chosen for people to need/greed/pass on. And voila. Whether there is one class or a hundred, each with their own gear, they'll get at least a piece.

Another example is trading. Have X pieces for other classes?! Exchange them for a piece from the set of a class of your choice. And suddenly, all those "failed" runs where all you got was gear useless for you will net you that one piece you wanted.

This is a problem in the players and developers heads (manifested as a result). It's not a problem in reality. I have no idea why people still, after all the MMO's out there, after all the solutions (some of them having part in this very game!) already found, still think there is such a problem as loot pool.