Risk reward my friend. In PvE there is no reason to use one. Weak enemies can be killed with primary weapons and strong enemies won't die quick enough. Plus the prevalence of light switch in higher level activities such as nightfall and weekly strikes makes getting into melee range suicidal. I do hope that this buff makes them more viable in PvE and less prevalent in PvP. I use a shot gun in PvP myself...but only because I feel that the weapon balancing forces me to use one.