Well. Your math sucking besides the point, the Frost DK buff was a PvE one. The PvP changes all came out later. Generally speaking the buffs have nothing to do with each other.
In this case, yeah, FDK might have seen a small buff, the sentiment is that the devs think that FDK needs a nerf and not the grossly overperforming Mage/Pal/Warrior meta trinity.
The basic combo of a frost dk is to get 2 enemies together, leg sweep/dragon stun/blind them or w/e, then let their chill streak bounce between them (this build stacks mastery just for this purpose) while doing your burst dmg.
The chill streak done this way is very very strong, ngl.
Yeah, I know what they do and the general theory behind it, but I don’t know how the numbers bear out exactly, because it does lose 10% damage, but does it also gain 5% as mentioned? Thus the net nerf is 5% on the CS for a 5% everywhere else? In which case you might make the damage up with just limb+breath?
Afaik because Chill Streak is a PVP talent and not a normal ability that’s built into the frost dk kit or normal talents, it would not have received the 5% buff.