Words can't describe how bad this idea is. You want an already generally good class to be twice as good, perhaps the even more dominant class in Helmet Heroes?
It's clear that most people (p2w to be exact) sway towards cowboy because of it's ease and constant damage, so why make that twice as easier.
If cowboys have 2 guns, archers get 2 bows, and then warriors and mages can hold 4 wands and 2 staffs or 2 - 4 swords.