I seem to have confirmed with further research that people do achieve good performance gaming or using other GPU-intensive apps on the right virtual machine setup (KVM/QEMU with VFIO GPU passthrough). Supposedly, performance could approach 95–100% of bare-metal in a well-tuned configuration—near-zero overhead with proper CPU pinning and HugePages. Impressive.
Based on this, it looks like modern VMs are a better solution than my experiences years ago when I was into Linux experimentation. I may be able to make the most of a stable, secure Linux desktop and keep some Windows apps + games around without much trouble after all.
Valve Proton has done a lot to improve Linux gaming, but it's not the perfect solution for every title yet.
That's to say I'm not just paying lip service to a potential switch to a Linux distro on my main PC. I'll start soon by playing with live ISOs to dip my toes in the water.