What is missing?

In #3351 and #3420, we introduced and refined endpoint discovery. As a result, we now pull version information from APIs unless using one of the legacy service types with the API version encoded in it. This should result in a single additional API call per service client, but we are not currently caching the result, which means we end up making an additional call for each actual call. This should be addressed in v3 and, ideally, the solution backported as a follow-up for #3435.