Why not? 1Password is built on the assumption that your vault could be copied by an adversary at any time, a 1Password account is even theoretically more secure

Why not? 1Password is built on the assumption that your vault could be copied by an adversary at any time, a 1Password account is even theoretically more secure because in addition to needing your master password they also need your account key which can only be retrieved from an existing device (or your recovery toolkit that you promptly printed and stored in a fire safe, right?).