> You can scale incredibly far on a single node

Nonsense. You can't outrun physics. The latency across the Atlantic is already ~100ms, and from the US to Asia Pacific can be ~300ms. If you are interested in performance and you need to shave off ~200ms in latency, you deploy an instance closer to your users. It makes absolutely no sense to frame the rationale around performance if your systems architecture imposes a massive performance penalty in networking just to shave a couple of ms in roundtrips to a data store. Absurd.

You need regional state, or you're still back hauling to the db with all the lag.

That only solves read latency not write latency. Unless you don't care about consistency.