I think you will find the weapons have been finely balanced. Remember playing Quake 1 with the rocket launcher? Anyone who had this weapon was pretty much invincible because it was waaaayyyy too good.
Reading Carmack's old plan files proved how much he wanted the weapons balanced. I seem to remember him adding in one extra shotgun shell to the shotgun at one stage.
The more difficult weapons are often more powerful, like the railgun which in the hands of a skilled player is often unstoppable. The same goes for the shotgun. Weapons like the plasma gun which require little/no skill to fire require multiple hits to kill someone. I think you will also find that the best overall weapon is still the rocket launcher. Remember that direct hits cause a lot more damage than splash damage.
Having said this I must say I am at a loss to explain the BFG10K. I mean sure it is rare but I mean... a cross between the rocket launcher and plasma gun which has a higher rate of fire than the rocket launcher? I can't see how this is balanced. Perhaps it is just meant to be an equaliser like a powerup or something.
Needless to say though, it is one COOL weapon!
