Wasn't the idiomatic way the `-v` flag (repeated for verbosity). And then stderr for errors (maybe warning too).

It is, and all logs should ideally go to stderr. But that doesn’t let you pipe them to different places.

Yes, but sometimes you want just important non-error logs to go to the console or journal, and then those plus verbose logs to go to a file that gets rotated, and then also stderr on top of that.