I think it may be down to perception as much as the changes. Snipers require a more skilled hand to use effectively now, i.e. you can't face off with someone coming at you with a primary due to the changes in flinch like you used to, but on really it would only require a bit more practise to over come. Most people, me included, switched to HC/Sniper loadout in year 2 because that was the dominant meta. I exclusively ran TLW/1k stare until just before RoI. Like everyone else I had to practise that load out to become effective with it. Anyone could have continued with that load out after a short period of practice, performance would dip but then even out again. In reality what happened was Bungie put out the message that snipers were too effective so were being nerfed. At that point people know they will now require adjustment in play and more skill to use so start thinking of alternatives in the special slot. Snipers dry up in most game modes and maps, shotgun rises up and there is a new meta and the majority switch to it. We all knew it would happen at some point. Destiny 2 PvP will bring with it a whole new meta too. I'm sure will see at least one new meta change in RoI. Perception can be very powerful in shaping opinion.