If you look at
https://www.warcraftlogs.com/statistics/10/# it shows both Unholy and Frost in the top 50% of specs overall aggregated across all bosses with Unholy edging slightly ahead. Both specs are in the upper end of mid-table for damage which is a perfectly fine place to be. The difference between the two specs is less than 2% which is small enough that it certainly seems fine to play whichever spec you prefer and play best at.
It will be interesting to see if they use this weeks numbers to make any adjustments. Shadow priests still seem to be a rather ridiculous outlier, they could knock a flat 15% off of shadow priest damage and the spec would still be in the top 50% of damage specs. They could easily make a few hotfix adjustments before nighthold launches, if they just brought the top four specs down (shadow priest, affliction warlock, fire mage and havoc DH) down and pushed the four worst contenders up a little (all hunter specs and enhancement shammie) they could have a spread across all DPS specs of 10% going into nighthold which would be fantastic. The min-maxers would still complain of course but if the different between the worst DPS spec in the game and the best was less than 10% overall that would be pretty hard to criticise.
For DKs however, based off of one day of data they are doing fine, not the standout by any means but both specs are edging their way into the top 50% of specs overall.