I was just thinking the same thing. Hmm..... Seems bungie is contradicting their previous statements a bit.

Why did you “nerf” my favorite weapon? Why not make the other ones better and leave mine alone?" Good question! Here’s why: We pay close attention to kill times in all game modes against all combatant types. If we brought up all the other weapons to account for lethality spikes that occur in specific situations, then our TTK (time to kill) would get faster with every patch. It is important to us to keep TTK values such that your arsenal feels lethal, but also both allows for some drama while you fight, and creates opportunities for counter-play when you’re being attacked.

Because according to the statistics that you either ignored and clearly can't comprehend, auto rifles are the most used. They don't want one gun type to be used more than others. To equal things out, they're making ARs weaker so people have more incentive to use the other gun types.