If you head over to the AMD forums you'll see that many users are reporting issues with AMD GPU's and DayZ. I recently bought a 6700 xt because my old 1070 died (rip) and I was excited to play DayZ with a new and stronger GPU. My happiness was short-lived as I quickly discovered the game ran worse than it did with my 1070. It's like the GPU doesn't recognize DayZ as a game and the GPU utulization varies between low 10's up to 99. While in the forest the GPU is alive with spinning fans and high GPU utilization hits 95-99% but once you go near a city the GPU decides to go to sleep or something and the game gets borderline unplayable. From over 200 FPS down to 50-70 👍 If I change the overall settings to poor the game works alright but then I can't see through windows beyond like 20-30m or something (it's a short distance) which is awful, so I raise the texture quality but then performance drops..
Maybe your game runs fine now idk but what you're describing is a reality for many many AMD GPU DayZ players and has been for a long time. I'm gonna sell this piece of crap GPU and never EVER buy another AMD GPU again.