At work, we're also Mongodb users. If tomorrow we try to benchmark against Cassandra, performance will probably be the selling point. I don't think it's absurd to compare mongodb and rethinkdb, they're very similar dbs.

As for the benchmark, I agree it doesn't explore every facet of both databases and focus on performance... That's what benchmarks do.

The intent of the author may have been to challenge his existing choice (mongodb) which is a good thing. The (corrected) results may lead to: expect no performance gain if we migrate to RethinkDB... What's wrong with that?