Frost was plain garbage in ToT. Blizz didn't forsee festerblight and it was an insaely strong dps spec until they nerfed it a while later. Frost 2h was beyond redemption and dw was the worst melee spec in ToT, with melee generally being the weaker half during that tier.
Only very few frost dks even managed to do reasonable damage compared to unholy and that mostly happened on famr when it didn't matter anymore at all and unholy was nerfed significantly. Ji-kun was a brilliant fight for unholy, since you could snapshot dots with the buff + feather and have an insanely strong dot for the entire fight and while elss frequent unholy also had more burst than frost.
I don't see what advatages frost had on primordius, unholy could bring more damage overall and Hb cleave wasn't a thing for that fight. Megaera also, snapshotting wasn't as strong there but still decent enough, maybe frost was viable there but from an optimization pov a dk would better be benched than having a froist dk for that fight because frost was weak.
Iron qon is also not favoring frost, you could get snapshotted dots on Qon on hc when he switched mounts, you had pretty strong cleave with snappedshot dots in the last phase and also more burst to nuke the important parts of the fight.
Overall, even when frost was better than unholy for some time it was all around at best middle of the pack. T14 was a tier where frost was reasonably strong but you could see plenty of fall off with 5.1 when they introduced item upgrades and was trashed with ToT as frost was carried by the strong t14 set bonuses until that point.
ToT was one of the weakest tiers frost ever had, if ever entered heroic.
In SoO frost was better than unholy for a short amount of time until they buffed unholy and even then, there dks playing unholy during progression amogn the world first racing guilds, only fight were frost really could call out unholy was blackfuse on belt duty, because pets bugged and frost had more frequent on demand burst, if you weren't on duty unholy would again better.
Unholy also won fights like Lei-Shen and Garrosh per default because of stronger execute and the ability to backload damage by exntending dots for a massive amount fo time to be able to fully nuke a boss in the lats phase, which were limited by time like lei-shen p3 and garrosh p4. Frost had a slight advanatge on the garrosh transmissions but not very strong either, so if you really had problems frost might've helped your raid there but for the rest unholy was clearly better.
HFC was the first time that frost looked decent since quite a while and they butchered it entirely instead of minor adjustments that were needed to bring in line for the world first race, since with gear it wouldn't have needed a nerf at all.
110 might give us a new chance, but if that chance isn't visible right now on beta I wouldn't get my hopes up. I personally haven't really played beta, so I can't really judge that.