Here is the quick and simple reason why they are strong.
They cost one point in the pick 10 system.
Here is the long reason..
Back when the devs had a play with devs community play date a month or so ago, people asked that question. David said it was because of the fact they use 1 point just like any other weapon. So for balancing reasons because of that cost they could not make them weak for it would be a waste of that one point if they did so. So they made them strong enough to be worth that one point.
Just because in past games pistols were weaker does not mean that in all games ever made they always have to be weaker.
The pistols are more realistic is what they are I think, I mean come on if you had a freakin pistol in reality and shot someone from say 300 feet away (long range in a map) one shot would probably kill, depending where you shoot them. But I bet you the bullet still goes right through the body. Its just more realistic for HC. I like that they did that.
They have the range of a shotgun, they lose to a shotgun, and they have low ammo. That's far from over powered.