The github repo mentioned this wiki article for multiplayer performance tweaks. Did you run through this list and make the recommended changes?

https://satisfactory.wiki.gg/wiki/Multiplayer#Engine.ini

Zabbix
https://www.zabbix.com/

Netdata
https://www.netdata.cloud/

Nagios
https://www.nagios.org/

SeaTools is a long-standing, trusted tool for HDD testing. I always have a bootable drive with the SeaTools bootable image on me for diagnosing hard drives.

https://www.seagate.com/support/downloads/seatools/seatools-legacy-support/

Keep in mind that testing a failing drive will likely make a failing drive worse. For your use-case this is fine, but for anyone else looking to test drives, please create a backup image of the drive prior to testing.

I play FFXIV and Warframe. I don’t have a PSN account and crossplay is fully functioning with both Playstation and Xbox users. Heck, Warframe is even available on Switch and crossplay works just fine with those users without any account linking.