It's full E2E encryption even without that turned on. However, just because something is encrypted doesn't mean it's secure, as you point out.

Regardless, governments/organizations have gotten very good at finding vulnerabilities and exploiting them before academic and/or private sector security groups discover the same vulnerabilities, who will then go and publish their findings which eventually leads to them getting patched. As a side note: For anyone interested in some modern hacker/cybersecurity history, I recommend reading the book, Sandworm by Andy Greenberg. It's pretty damn wild what it covers and that's only a fraction of the modern state of global cyber warfare (and yes, just about the entire world has been engaged in what pretty much amounts to cyber warfare/espionage/sabotage for the last 10-15+ years).