Originally Posted by
AlphaDragoon
As for how they can make it difficult without having speed runs, they could do a number of things. Just as an example, as people have already said on this very thread they can make optional bosses within dungeons that are required to unlock the higher level chests. Or make conditions on the boss, like a boss with multiple body parts (that could require different strategies to kill, such as one being resistant to magic and another to physical attacks) that you have to take out before killing the boss himself to get the full clear.
Speed runs are just the easiest and the lamest way to add artificial difficulty and they need to stop relying on it.