Mach was designed to make clean separation between operating systems and hardware. Notice how easily Apple moves between hardware? The unsung hero is Mach and the design patterns that NeXT/Apple framework built on top of it.

That is largely due to a mix of Apple's investment in emulation technologies, and Apple's ability to exert influence on third party developers and vendors to keep up with their latest tooling. Very little to do with the Mach kernel.

The ability to move between hardware platforms also has very little do with the ability to run operating systems in virtualization. Case in point is that Apple is one of the last major OSes to include a hypervisor in the OS.

I'm certainly not an xnu specialist but from what I understand, you've basically got a BSD kernel (a "macrokernel") running in privileged mode that (roughly) just has a few services replaced by or connected to Mach ones. So I'm not really sure they get much portability benefit specifically from Mach versus "more traditional" kernels.

It’s easy from the user’s point of view. It’s not easy to write Rosetta.

Every modern operating system was designed to easily move hardware. (It also helps a lot that all hardware is basically the same thing.)

There is nothing special about Mach/xnu here and it is not helping anything.