This is mostly correct but primary keys have to co-exist with the existing data infrastructure that is unlikely to be replaced for decades. It is quite possibl

This is mostly correct but primary keys have to co-exist with the existing data infrastructure that is unlikely to be replaced for decades. It is quite possible to do cluster-style indexing on UUIDs through disk on a single server at rates of tens of millions per second, I do it every day, just not with your typical ordered-tree architectures. Many popular database engines are not designed to make this particular scenario perform well.