[WorldMaker]

This sort of suggestion is for that worst case that you already have brownfield consumers that don't care about the signature using outer fields and you need to add the signature without breaking those consumers.

The redundancy is absolutely a recipe for disaster, but so is the part where you have brownfield consumers that you can't break and know that they also don't care about message security.

Unfortunately, it's an all too common brownfield to find yourself stepping into, which is why it is such a too common ask for "inline JSON signatures" (or other document languages like XML) that don't change the outer shape of the JSON document to break backwards compatibility with dumber consumers.

Also, unfortunately the most correct answer in cryptographic practice is also often the hardest to sell to those consumers (or to business people prioritizing changes to them): break those consumers and force them to care about security so that a rising tide lifts all boats.