Well, the Monk was given absolutely nothing that it's good at. Oh, wait, it can run fast. Except that running fast doesn't solve a single problem or contribute anything at all to the rest of the party. That's what I mean when I say that the designers didn't expect it to be played, well that and it didn't fit the balance paradigm that they built the rest of the game around.
The expected party is Healer, Blaster, Tank, and Trapfinder. But then of course, one member of the party also needs to be the "Toolbot," which is the role that deals with esoteric situations like invisible foes, or interdimensional travel, or other odd things. This is more a "fifth wheel" type role, but it is not enough to focus a class around.
Classes like Barbarian, Ranger, Sorcerer, and Bard do not fit the expected party roles and thus their balance was an afterthought at best as it pertained to the balance of the rest of the game especially.
And then of course, basically no class other than the Rogue actually functions in its intended role and the Rogue's intended role is really lame. Literally, if the Expert NPC class had Trapfinding it would function equally well in the role the Rogue was intended to fulfill.