You're missing xpensive's point here.
Ross Brawn was involved in the technical regulations surrounding the diffuser regulations that were coming into force in 2009, as well as Chairman of the OWG in a way that can be best described as compromising. It's kind of like putting a fox in charge of designing chicken coops, but I suppose Brabham's ex-spanner, three decimal places man couldn't be trusted to do it which is why we ended up with FOTA's technical working group.
Newey never wrote any rules on flexible bodywork as xpensive says, so the comparison is just not valid. There's a difference between finding a loophole in regulations you didn't write, because that takes foresight and effort, and engineering a loophole you already have in mind into the wording of regulations that you are writing.