Nothing wrong. GCN based GPU was never good at OpenGL. Vulkan was MADE to address this. All GCN GPU are pretty bad at keeping the compute engine fully utilized due to bad scheduler efficiency. Vulkan and DX12 removes the burden and allows close to max stream processor utilization, hence why a lot higher scores.
I see very different behavior in OpenGL games. Vulkan is much faster, of course, but it's not because the GPU isn't being utilized in OpenGL, like this benchmark shows. I just tried it in Doom, which supports both OpenGL and Vulkan. Set to 4k, ultra, load Kadengir Sanctum, observe framerate, load, and GPU clocks for 1:30->
Vulkan: 99-100 FPS, 1627 avg GPU clock, 99.0% avg GPU Utilization
OPENGL: 65-66 FPS, 1629 avg GPU clock, 97.3% avg GPU Utilization
To add, looks like there's something funky with AMD's OpenGL implementation specifically - see:
https://community.amd.com/thread/206176 -- mentions the relatively very poor performance, as well as talking about the low GPU clocks I'm seeing. In that thread there's some theory that maybe it's being locked to a CPU-bound thread, but that doesn't seem to be the case here (I'm not showing any CPU threads maxed out), and it looks like they came to the same conclusion..
But I guess id found a way to work around it? Doom OpenGL definitely isn't suffering from the same problem.
I guess the fact that I couldn't find any other games running openGL in my library means I shouldn't be too worried about it, though.