Why insist on clambering to the belief the designers can do no wrong?
That's not what I have done.
I have said nothing regarding whether the designers can, cannot, did, or did not, do wrong.
I have said that a DM, as an integral and inherent part of being a DM, is the one responsible for choosing which rules to use, which not to use, which to change, and how to change them, to satisfy their own and their group's enjoyment at the table.
And to make this as fully and finally clear as I possibly can: Yeah, it's not a great idea for the authors of an adventure to write-in the assumption of using a particular optional rule. It's also not great to implement that optional rule in a way that easily promotes a negative view of that particular optional rule.
But most of all, it's not great for a DM to feel their authority over the rules actually used at their own table is overridden by any author - especially, and I cannot be more emphatic about this, those authors that particular DM feels have done wrong.