I can confirm this works on Cassandra 3.11.6: https://www.robustperception.io/monitoring-cassandra-with-prometheus

so, for now, I can use that and not the packaged CentOS version, though figuring out what the hell is different about the packaged version is probably a good exercise for understand this. Cassandra is one of the things we are week on in the team (though not java, that's a personal weakness). While I am obviously going to be the SME for monitoring, I think I am going to end up that way for Cassandra as well just out of necessity.