Wat? I play games all the time on my Windows 10 + WSL2 setup.... which is exactly as I described: Windows running as a guest under Hyper-V alongside Linux.
[0]: https://lore.kernel.org/lkml/20200914112802.80611-1-wei.liu@...
And I can have running wsl2 session with RDR2 running.
as far as I can tell, enabling wsl2 (thus hyperV) did not slow down windows in any meaningful way I could find.