The point of ReactOS wasn’t to keep up with windows but to maintain a useable subset of windows API. They have done that.
Really the scary thing they have done is reimplement windows NT entirely (!)
Whats almost crazier is that this is not the first time this has been done! The WINE project is almost the same thing, just running atop a *nix OS instead of on bare metal, and the long-forgotten SoftPC and SoftWindows virtual machine/emulator (to run DOS and Windows, emulated, on a classic Mac), which apparently trapped and executed natively a few Windows APIs, so that they didn’t have to be run in the emulated 486 CPU. Wiki describes it as “Unlike most emulators, the SoftWindows product used recompiled Windows components to improve performance in most business applications, providing almost native performance (but this meant that, unlike SoftPC, SoftWindows was not upgradable)”. The “almost native” claim is, uh, let’s call it a slight exaggeration. I’m not entirely sure whether Insignia, the developer, wrote those themselves or licensed them from Microsoft, which apparently is a thing.
Not to mention that the Win32 API itself was implemented by Microsoft itself three times: once atop DOS (in Win 3.1—Win ME), once atop NT (itself being a clone of VMS), and once atop Windows CE. The Win16 API was implemented at minimum on the first two.
And just for comparison, Apple reimplemented the original Mac APIs, slightly tweaked, as Carbon running on UNIX in Mac OS X, but also as a runtime library for Mac OS 8 and 9. Similarly, prior to being acquired by Apple, NeXT had its native APIs running not only on NeXTstep/OpenStep, but also as a runtime library on Windows.