The supported values for the "level" field are currently these four:

https://github.com/openshift/cluster-logging-operator/pull/1203/files#diff-620fda7d1a46cb683279924b35812d0258cb5e03dee12c3f60ec4bd93a61ad9aR478

Our documentation implies a larger set are supported:
https://docs.openshift.com/container-platform/4.8/logging/cluster-logging-exported-fields.html#level

The defaults should be expanded to match the documentation, or else the ability to pick/choose level values would be useful (to allow administrators to trade off between more coverage vs better performance)