(I worked at Coinbase a little while back)
Your coins are not safe/secure while they are with coinbase, and will never be because you do not own the private keys. It does not prevent you from losing your money in the event of worst case scenarios, it just makes it harder for someone to steal your money while it is in the care of coinbase.
This is the part I was responding to. It sounds like you're saying that using the vault feature will move your coins into cold storage. In fact, they were always in cold storage.
I'm sure crypto projects and experience are a plus :)