It would have made more sense to just add another ‘grade’ to beef, rather than using a breed name. Call it extra-prime or something like that.
In my opinion a Holstein/Hereford cross is about the best beef you can get if it is raised right.
We always had Polled Herefords and some Charolais mix for size. The beef we raised for our own consumption was raised in confinement with a controlled diet, which produced a good marbled prime beef. The market doesn't pay enough premium to justify this effort and expense in large volumes.
There is a big difference between proper marbling and fat. What went to market was fat, what went to the freezer was marbled. :)