I am sure it was intended to be that way. But it is not like it is breaking the game to add Dex twice to damage, even if you tag on Charisma with Mysterious Strange at most if you had 18 in both scores you are dealing 12+1d8 damage at 5 on. Of course adding other things like Deadly Aim, Point Blank Shot, and Weapon Focus did do a little better to make it hit harder and more often but that can be said of any work up with feats.