I wouldn’t go that far. I mean, it’s not great that they have the liberty of writing a vague or minimal standard for themselves. But at least you can hold them to their own standard. And in situations where there is no standard in place, you can argue that your CFREU Art.41 rights are generally undermined.
A good judge would treat an unwritten standard in favor of the complainant. There is a legal concept in contract law that says the benefit of vague or ambiguous terms in a contract goes to the party who did not draft the contract. This principle punishes the side who had the advantage of writing the contract for their negligence. Hopefully a similar concept would be considered in the case of good administration. Not sure if this principle exists in Europe or how realistic that is.
I have encountered several cases where a Belgian administrative office violated the Belgian standards. In principle I can escalate a complaint on that basis. I would not consider this useless.
Thanks! IIUC (from a machine translation), there is no code of “good administrative” conduct for Germany: