My team were doing crota with 4 people all lvl 34 in 2 swords yesterday. The three rocketers had maxed 365 galleys and 3 rockets ripped the Shields away. That if ablnything going forwards is the reason for the nerf. Assuming exotics can be ascended in ttk, imagine the damage a 400 Gally can do after September, or even worst a 440 or 484 Gally afterward a couple more expansions. Destiny nerfs level so a lvl 40 character does the same maxed damage as a lvl 34 against lvl 33 crota, while the guns base damage keeps going up. I think is is why they are changing guns, they realised that continuing this path players will soon be able to one-shot crota or atheon.