I'd say that no, a range query probably isn't the best for monitoring, but it really depends on how important it is that the range you select is consistent.
>From those traces it does seem that the bulk of the time spent was waiting for responses from the replicas, which may indicate a network issue, but it's not conclusive evidence. For SSTables you could check the SSTables per read of the query, but it's unnecessary as the traces indicate that's not the issue. Might be worth trying to debug potential network issues. Might be worth looking into metrics like CoordinatorReadLatency and CoordinatorScanLatency at the table level https://cassandra.apache.org/doc/latest/operating/metrics.html#table-metrics Also if you have any network traffic metrics between nodes would be a good place to look. Other than that I'd look in the logs on each node when you run the trace and try and identify any errors that could be causing problems.
