An immutable OS install and app sandboxing by default provide a lot of security. Those are present on third-party Android distributions that don't pass SafetyNet. Some users of those add root access so they can let a handful of apps out of the sandbox, but I'm willing to bet most of those are tech experts with better security habits than the average person.
Show me examples of actual data breaches and account takeovers SafetyNet would have stopped if you really want to defend this position.
It's just a way for app makers to point their finger at someone else.
No, Play Integrity labels those old systems as secure, _even though they are not secure_ due to lacking years of security patches.
Play Integrity does not prove that something is _secure_, only that the OS that is running _was approved by the phone maker_.
This is the crux of your entire argument, so you kind of need to actually substantiate it. Does Play Integrity catch an app from to Play Store using an exploit against a comically ancient vendor kernel to do anything it wants? How?