There is no mapping of logging module log levels to Apache levels as it would cause various subtle problems which would leave you scratching your head as to why you are not getting log messages from Python because of the Apache log level overriding things and suppressing output.
What you are currently getting is because the logging module is simply logging to stderr, which under mod_wsgi gets logged in the Apache error log under 'ERROR' with Apache sticking its own log message prefixes on each line.
You can still use an output formatter to control what you see in your part of the message, but you cannot replace the prefix Apache places on each line.