You claim that MySQL 8 is ahead when it comes to scalability. What are the bases of this claim? When I see comparisons or entire systems that rely on a database (that is, not micro-benchmarks) such as the TechEmpower web framework benchmarks [0] , I notice that the 'Pg' results cluster near the top, with the "My" results showing up further down the rankings. I understand this isn't version 14 of the former versus version 8 of the latter. But it makes me wonder what the basis of your claims is.
Techempower is not a database benchmark. The tests that involve a DB exist to include a DB client in the request flow, not to put any serious load on the database.
Aren't those run on a single node DB server? And the queries don't really seem realistic at all, e.g. single query test fetches 1 out of 10 000 rows, with no joins at all. Fortunes fetches 1 out of 10 rows. This seems extremely trivial.