It does seem that Microsoft is making it more difficult for third party hypervisors. I’m beginning to think that the biggest cause of performance issues with Workstation is Microsoft’s foot-dragging. I think the Workstation issues reported here when using Hyper-V as the hypervisor on Alder Lake CPUs is that Microsoft isn’t opening up things in Hyper+V APIs that would let Workstation run better.
Theres a similar effort to take over the hypervisor space over at Apple, but the big issue there is with virtualizing macOS on Apple Silicon. Apple will let you do it, but only with another API set that doesn’t have the functionality of the API set that Parallels and VMware use for Windows and Linux.