what you are saying is all true, however in this case he's actually getting better performance from his hackintosh then from running windows on the same machine. I am more suspicious that there is something wrong with his Windows configuration.
Comparing someone's 2019 hackintosh to a 2012 MacPro is not very useful information for this discussion.
Another factor is that newer CPU's have certain low level CPU instruction set optimizations in them which Cubase or VEP could be using, which a 2012 MacPro cannot take advantage of, and on and on. Perhaps Cubase is coded somehow to take advantage of newer CPU's which are more common on windows by the way, while not being optimized for 2012 architectures, which like it or not are much more common on the Apple community at this time. Just thinking out loud now.
It would be interesting to have a 2019 ImacPro, or the next gen thing coming out this year, tested with both OS X and windows bootcamp, to see how they compare, but ultimately I would still expect Cubase to be highly optimized under windows and less so under OS X just because of Steinberg's history. But its possible they are getting closer and closer to performance parity between the two platforms when the same hardware is used.
What I can say is that here in my studio with my ancient 5,1 Mac Pro, Cubase10 does not perform well at all, LogicPro is performing 3x better. That is true with and without VEP involved in the setup. I can't imagine that a windows setup would perform worse then what I have, but maybe I would have to install bootcamp to find out for sure, which I don't plan to do.