I'd just like to remind everyone that Strifeload's opinions are heavily biased due to 3 simple reasons:
a) He has the Unholy bis legendary (bracers), therefore, Unholy being undertuned isn't a big problem to him
b) He's not any sort of serious PVE player. Pretty sure a couple weeks ago he mentioned he had killed Heroic Nythendra in a pug as if it was an accomplishment.
c) Following b), this also means he is severely undergeared in the PVE scene, which makes the Unholy scaling issue seem less apparent to him.
So if by any chance, you want to be doing some sort of progression in an organized guild, you should re-evaluate your decision to pick DK, as right now, even if Frost damage is alright, it brings very little else to the table in terms of utility or movement. If all you do is LFR, just play whatever you like and enjoy.
And just to add, all you had to do was look at the 3rd post in this thread if you wanted an actual educated opinion:
Kanj got World 3rd Mythic Helya kill as a Frost DK, first DK to do it in a legit way (since the others had their kills removed). When he says something like this, and you get no-names telling you that the DK world is perfect, you should probably re-think who to trust
Also, grats on the kill Kanj, very impressive, the video made it look smooth af