Making a "Martial Artist" core class is filled with design problems:
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2> D&D "game balance" is predicated on equipment. This is a much more subtle point, but it keeps coming back to kick people. You see, Paladins and Barbarians are supposedly balanced against Wizards, Clerics, and Druids based on the concept that they have equipment. Magic Swords, Magic Pants, the whole thing. If characters don't have this sort of equipment, the warriors can pretty much go home while the druid doesn't even really notice. So a "martial artist" has to be balanced against a "knight" when the knight has a magic sword. Because if the game is balanced right now - the knight does have a magic sword.
So it's another damned if you do, damned if you don't design problem. If you write your Martial Artist so that he is actually balanced against a knight in shining armor with a magic sword - the class is unbalanced as he's just like the knight except he doesn't need the magic sword. But if you design the Martial Artist so that he is in any meaningful way weaker than the knight in shining armor with the magic sword - you've created a class which is ass, as in reality the knight in fact does have that sword.