I don't think that PRISM involved root access to any devices and this link does not claim that it did.

I was expecting this link: https://en.wikipedia.org/wiki/Apple%E2%80%93FBI_encryption_d...

still doesn’t really prove much

It actually proves that they _don't_ (or didn't) have that kind of access because they first publicly asked for the access and then rescinded that request when they, not officially but widely accepted, acquired access through some kind of hack/bug/exploit given to them by, probably, the IDF or an Israeli private company.