[obnauticus]

Somewhat depends on your threat model. The relative value of an iCloud/aws/gDrive 0day is going to be higher than Nextcloud. If you’re in the category of people concerned about this type of breach, self-hosting a PHP web app and claiming it’s somehow safer wont save you either. For this risky population, neither solution works since attackers are willing to throw expensive exploits at your data in either scenario.

If you aren’t being specifically targeted, then you would care about low hanging fruits discovered by something like automated scanning. Not exposing your service to the internet does solve this assuming you’re confident in the stack which provides this isolation. But managing this stack and performing risk calculus here is actually where the security horse trading happens. I think most people aren’t safer managing this themselves — arguably they’re actually worse off.

I have high standards for the confidentiality of my data. I care about things like lateral movement and the massive attack surface that isolation tech to prevent such movement has. I also won’t design monitoring and alerting, ensure a patch state, or perform code audits on Nextcloud and all the isolation tech required to secure it to a comporable level of security. Because of this, I instead reason around the cost of exploitation. I want it to be higher than what I believe Nextcloud provides and I’d rather require an attacker to use an expensive 0day to extract my data off a cloud provider like Google versus a potentially cheap one against my own infra.