There is nothing in here that justifies not using sealed secrets, it's filled with incorrect information and opinions. The evidence such as TLS encryption strategy proves sealed secrets work, not that they don't.

Credential rotation, come on, if you have this problem, then you have this problem, it's much easier to rotate credentials in code than in a UI/repo somewhere, it also get's you a free audit trail.

Multiple environments, WHAT!, there's no different on what you would be doing with non-sealed secrets. Encrypt/Decrypt the secret at the right place.

This article is just bad advice.