Fail2ban could be potentially useful in an era of passwords, especially when systems allowed anyone to login remotely, and you only had the one server because servers were very expensive.

However, the moment the industry went to SSH Keys en masse, and got away from passwords, fail2ban stop serving any real purpose other than to make people feel like they had done something to improve security. Which it didn’t really, especially if you enforced key usage only for logins.

Literally, the only argument you can make is that fail2ban might reduce the number of log entries.