Abysmal performance certian games

[FawnPoem]

So I have an old(ish) gaming machine that I'd like to repurpose as a spare VR rig. It runs regular games just fine (Fortnite, Beam NG drive, Minecraft) but when I try to play VRChat (In desktop mode) I get a solid 10 FPS as if there is a frame rate cap. Single threaded CPU usage is near 100 on a single core and the GPU is only being used by about 11-18 percent. I confirmed it's not a heat issue. The specs are listed below:
CPU: AMD FX-8320e @4.2GHz
GPU: Radeon R9-285
RAM: 8GB Viper Xtreme

I know that AMD FX is showing it's age but I'd at least expect 30 FPS in VRChat. This isn't an issue on my Ryzen 7 system.

 

[rgd1101]

MERGED QUESTION
Question from FawnPoem : "Unrealisticly Low Framerate in VRChat"

So I have an old PC that I'd like to setup for VRChat whenever I have a guest over. I would open VRChat in desktop mode and then enter the home world which isn't as demanding as other worlds. I end up getting 8-12 FPS from just standing there. I would at least expect 30 FPS considering the specs. The CPU usage sits at around 12-30 percent usage while the GPU sits at about 5-15%. I've tested other games such as TeamFortress 2, Fortnite, BeamNG drive, and minecraft and too my surprise, they ran just like how I would expect them to. This issue doesn't happen on my Ryzen 7 rig. The PC's specs
AMD FX-8320e @4.2GHz
RAM: 16GB Viper extreme memory 4x4
Graphics card: Radeon R9 285 4GB

I also noticed similar behaviour from an AMD Athlon 5350.