Yes I like cookies but no you are not just wondering why you would decrease the rate of fire on the snipers. You coupled it with the 870 having too much range. That is the whole of your arguement as presented. Now if you'd like to change your arguement to only be about decreasing the rate of fire on the snipers and leave out the rest, I would be happy to discuss that as well.
The reduction of fire rate in the snipers was to reduce the feeding opportunity for the DSR mainly given that it has a rather large hitbox and the Ballista was reduced only slightly. Personally, I didn't have a problem with either weapon as was. However, there is a rather large community rejection towards QSing being so easy and this is what the devs decided to do to address the obvious imbalance (compared to how all of the other weapons are restricted) in the snipers. Again, this change wasn't needed in my opinion and it did nothing to alter the ease of QSing. So I wouldn't have bothered with it. All that being said, the DSR and Ballista are still very deadly weapons in the right hands and the nerf isn't worth worrying about unless you make you living off of feeding montages.