> Is it really true that concerns around UUIDs as primary keys are wholly irrelevant?
I would say yes, with the options we have today with modern compute.
We live in a world where compute is powerful enough to enable Let's Encrypt to issue SSL certificates for 235 million websites every 90 days off the back of a single MySQL server[1].
For high scale environments there are also other options such as async queues and Redis middleware.
Database technology itself is also evolving, and the degree of measurable downside is less than it might have been 10 years ago.
I would still argue that for the vast majority of people, UUIDs are the way to go. I would certainly urge caution against premature optimisation involved with the "but high scale" argument. Sure things MIGHT be noticeable at high scale, but I think its fair to say most people are not doing anywhere enough high scale to do so and should probably just use UUIDs and cross the "high scale" bridge if/when they ever come to it.
Finally, its also worth pointing out that all the hyperscalers use UUIDs or other unique identifiers widely in their infrastructure and APIs, all of which must inevitably be tied into a database backend.
[1]https://letsencrypt.org/2021/01/21/next-gen-database-servers...