I generally agree with you. However, Michigan's new POA statute provides, in part: "(e) Unless provided in the durable power of attorney or by judicial order, the attorney-in-fact, while acting as attorney-in-fact, shall not create an account or other asset in joint tenancy between the principal and the attorney-in-fact."
There is also case law to the effect that it is improper for an agent to change the nature of the principal's accounts. In other words, if the principal has accounts that are all supposed to pass to a certain beneficiary, it would be a breach of duty to close those accounts and place the funds in accounts where the agent is listed as beneficiary, for example.
The laws are not perfect and there is not very good oversight into these matters. So care and caution are still very important when selecting an agent.
Thank you for your MI specific clarification. Very informative.