I don't think Kafka using eschewing fsyncs is a bad thing; I'm aware of the risks. What I'm pointing out, and what got Mongo killed in the court of public opinion, was saying "our database is blazing fast because we turned off fsyncs".
Benchmarking a system that fsyncs every write to one that doesn't isn't an apples-to-apples comparison. You are free to make the argument that you might not need them, but if you are benchmarking systems and one of them fsyncs by default, that is the level of durability I'm going to expect, otherwise I can assume the other guy will be just as fast if he turns off fsyncs as well.
Benchmarking a system that fsyncs every write to one that doesn't isn't an apples-to-apples comparison. You are free to make the argument that you might not need them, but if you are benchmarking systems and one of them fsyncs by default, that is the level of durability I'm going to expect, otherwise I can assume the other guy will be just as fast if he turns off fsyncs as well.