Any keys stored on an internet connected device have way more vulnerabilities than keys stored completely off a device
Discussion
You can create a wallet with wifi turned off. Back up seed. Delete wallet.
Your Internet connected phone could already be compromised. There many ways to steal your keys from a compromised device. It's just a basic principle you don't mess with for serious sums.
Could this solve that issue?
But when you sign a transaction that would happen on an internet connected device still? Right? Or atleast you have to communicate with an internet connected device still?