I think these are different. They mostly find vulnerability in the iOS system as opposed to try to crack the backup system.
I think iOS or Android backup system are rather secure compared to other components because of the following: hacker will also need to break into a cloud drive to retrieve them, which adds extra work; the backup is simple, just bunch of files and a password, apple/google can use standard well-tested encryption to encrypt them.
However, guaranteeing there is no way to break into an operating system, especially with all the features that a modern system requires, is much harder.
First it uses lock screen password, so google do not have access to this password.
Even if your lock screen is unfortunately your Google password, I think proper authentication protocol do not send your password to Google to authenticate, but only the hash, which cannot be reverted to derive your password.
Obviously, the above is assuming that Google is not malicious. Otherwise it can just use play service, which is privileged and closed source, to get all your data. If your threat model including Google itself trying to steal your key, you will probably need to install a trusted rom or use iOS (however, apple and the rom developer can also steal your key).