This is absolutely true, but in some ways this is more about reducing the number of 'attempted connections' in the sshd log. Meaning, any failed connection that is recorded (and ideally shipped off to a centralized log system) is in some way actionable. Opening up port 22 (with keys) will still create tonnes of alerts from any SIEM.

The other thing to consider is that there could be exploits in OpenSSH itself. There hasn't been a truly critical vulnerability in a very long time, but low severity or non RCE vulnerabilities aren't exactly rare: https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=openssh