Logic behind the DPS classes?

[Ryans]

Ironically, internal damage is extremely dangerous IRL, more than many types of external wounds. Part of why you can literally take an arrow to your brain and survive, yet a single well placed punch will kill the victim (the 'king' hit being an example)

Yes, internal damage is the cause of a lot of deaths. The shock wave from an explosion has a bigger blast radius than the shrapnel, for instance, and can be just as deadly. But it isn't exactly fair to compare a perfectly placed punch to a target that isn't prepared to receive the punch to an arrow that was perfectly placed to NOT instantly kill someone. You are much less likely to survive being shot in the head than you are from having a ruptured spleen. The main problem is that people know when they have an arrow sticking out of their head, but many people overlook internal damage until it is too late.

[Sylve]

snip.

My point is simply that an internal injury is just as, if not more so, dangerous as external injuries, even arrows.
a Monk does a slow ramp up of damage, its multiple small hits with internal injuries going on that give it the damage output that it gets.
You can wear armor to mitigate impacts and such, but a strike designed to ignore that armor and inflict an internal injury is going to hurt. Even plate armor does not prevent damage to the body. Thats the essence of how a Monk does its damage.
One can argue that Mages and Bards aren't as lethal because the target has defenses against external attacks, but lacks the ability to protect its insides.