COPY api in Postgres avoids a lot of the query parsing and other stuff that takes up cpu time. I have used it in production and have seen great results.

There are cases where the COPY api is not sufficient. For instance it cannot do the ON CONFLICT IGNORE thingy and instead fails the call. In that case we fallback to INSERT ON CONFLICT IGNORE - since in our application we do not expect too many duplicates this works well for us.