Nah, I dug deeper into this. Right conclusion, wrong reasoning.
The reason KRaft turns out to be fine is because the KRaft topic does fsync! Source: https://cwiki.apache.org/confluence/display/KAFKA/KIP-595%3A...
KRaft is used for metadata replication in the same way that Zookeeper is used for metadata. I.e., in a very meaningful way.