The device stores the data for accessing the wallet... He doesn't store anything else!
Tell me more precisely what kind of data the hardware wallet stores and what it doesn't store?
And he would have succeeded if he had a seed phrase. Only if you have a seed phrase, you can restore access to your wallet and your money. For this, it was proposed to write down the seed phrase on a piece of paper, so that in the event of a breakdown or loss of a physical wallet, access could be restored.
That's good. So with the help of his recovery phrase, John can easily restore his accounts in the same or in a new hardware wallet. Can Mike the store clerk do it for him and find his seed?
Wash the cold key keeps only private keys in yourself, or am I mistaken?
Can you please explain this quoted part of your post?