Why is it a bad design?

The game have a lot of content for all levels and classes/jobs, so the logical thing is to 'encourage' you to try it all, and thats the reason why is not that easy to get to level 50 just by doing the quests alone (but I bet you can if you do ALL the quests in the game, tho).

So go and try the FATEs, levequests, hunting log and everything else, it's fun!