trying to create a role that already exists. At this point, my head is already kind of exploding, because I thought we were pretty careful to try to make it so that pg_dump output can be restored without error even in the face of pre-existing objects like the public schema and the plpgsql language, but apparently we haven't applied the same principle to pg_dumpall.[1]
This has always been my understanding, even if we are not explicitly stating it anywhere. pg_dump -> no errors. pg_dumpall -> always at least one error :)
But if, as you posit above, we were to try running the output of pg_dumpall through psql as a non-superuser, the problem is a whole lot worse.
I'm of the camp that pg_dumpall should almost always be run as superuser. That said, I find myself using pg_dumpall less and less with every year, and cannot think of the last time I advised a client to use it (other than a pg_dumpall --globals and ignore the errors as a poor-man's role duplication system. Even that is getting rarer, as we generally don't want the same passwords)
