The only way I get expected performance from Doom with an RX480 is to turn power efficiency off before playing then it stays at 60fps consistently with vsync, if I leave power efficiency on as I do with most games it really struggles with vsync frequently dipping to the low 40s and stuttering when it is at 60.
I'm not entirely sure if the RX500 series cards have a power efficiency toggle in the drivers (my eldest's 570 doesn't) but you could try increasing the power limit in wattman
Thanks, but it doesn't seem to really an issue of the card not delivering to expectations in my case, it's performance is right where it should be when I look at other Doom benchmarks for this particular card on the web. It's getting very close to a mostly-constant 60 at 1080 on medium with some extra features enabled.
The issue is basically Doom's wonky frame pacing with vsync enabled (which seems to be strictly double-buffered which is actually rare in games these days) and in situations this is where enhanced sync would be ideal for, but it just introduces even more stuttering, as it does in many games in my experience - D3D or Vulkan. This has been apparently been an issue for a subset of users since its intro.
However, I did find a workaround - RivaTuner Statistics Server. Basically I used this to limit the frame rate to 60, and kept Doom's in-game vsync on, and surprisingly this fixes the huge drops to 30-40fps it had before when the framerate would go under 60. It's still noticeable when it does, but it behaves as you would expect - slight stuttering as opposed to falling through the floor without it. AMD's own frame rate control does nothing for smoothness with Doom's vsync and only helps with vsync off, but then I still get some constant tearing. This seems to be the best compromise.