No; Unholy’s decline started with the Legion rework. Late WOTLK and WoD were Unholy at its absolute peak; Wrath because of how really freaking nasty Scourge Strike started to get with gear, and WoD because of Necrotic Plague and how it could be maintained at its biggest damage ticks for quite a long while. In addition, the way the rotation was set up you had an instance of “Ok, NP is up at full strength, I now have a full bar of Death Runes. Everything is set up; now I simply destroy you.” with 6-8 Scourge Strikes in a row, each one capable of multistriking at least half a dozen times; in addition, we also had our ghoul that could occasionally become big and angry. With Legion, the class fantasy of a dark, shadow knight whose necromantic energy ruined enemies gave way to a weird sort of grossout body horror of popping pimples and slime that seems like it came straight out of 90s era Nickelodeon. Now, 90s era Nickelodeon was pretty cool, but not the sort of thing I think of when I think “Unholy death knight”. I have long struggled to like the spec since.
Frost? I’ll tell you Frost’s biggest problem: Breath of Sindragosa. That ability needs to die in an eternal black fire. I hate it, have always hated it and will continue to hate it going forward: it is the Rune of Power of Death Knights. I do agree that Obliterate, for an ability with that exact sort of name, needs to be hitting much harder, especially for 2h Frost.