Probably because balancing conduits, legendaries, covenant abilities, talents, and abilities is an absolute nightmare and they thought it would legit be something simple to do. Instead all its done once again with borrowed power is to make the gap larger for whatever happens to be the fotm based on some arbitrary numbers they came up with without doing any actual math. PvP will never be fixed until all of its removed and we just go back to One Rank Honor/Conquest gear only and the only focus is balancing talents and abilities entirely.
As for Destro Locks, they will always be stronger towards the end of an xpac due to haste and various stat growth. But they’re so particularly strong now just because of all the extra stuff that Blizz had been tone deaf for, for years now. Every attempt to fix past mistakes with new systems will always fail, with 100% certainty. They refuse to backtrack and go back to earlier systems because largely those teams are just gone now and they don’t want to acknowledge past “mistakes”, because of their inability to have balanced those out, despite them being vastly more balanced than things have been for a long time now.
Dragonflight will hopefully fix a lot of this stuff and be a better move towards the future and back to the simplest of basics for the game, which is all it ever needed to be. There will still be problems and some balancing issues as always, but in general it should be hopefully better. If you still have hope for Shadowlands at this point, you’ve deluded yourself heavily.