I don't think it's hand-wavy. I think you're upset about something else related to Cassandra that perhaps you read recently -- not tlack's comment. Suggesting it would make more sense to compare an in-memory data store to another in-memory data store would be a more interesting comparison seems a perfectly valid suggestion.

"This is so silly. Wait -- hand wavy -- that's right, nothing can be compared to Cassandra but pure love itself."

C'mon, man. That doesn't further discussion. That sort of statement serves only to incite anger.