Mistwell
Crusty Old Meatwad
If you crunch the numbers on even the most rudimentary level, you immediately realize in no way can they do everything those other classes can do, even a little. Even with triple the Ki they don't keep up, much less with the very limited Ki they get. Their damage output at mid to higher levels simply cannot possible achieve what the other melee classes achieve.The OP provides a more reasonable explanation.
I really do honestly think this comes from someone's playtest bad experience.