My counter argument is that the entire web exists because of Postel's law. HTML would just be another obsolete boring document format from the 1980s. I agree

My counter argument is that the entire web exists because of Postel's law. HTML would just be another obsolete boring document format from the 1980s. I agree that there are better ways to design flexibility into protocols but that requires effort, forethought, and most of all imagination. You might not imagine that your little scientific document format would eventually become the world's largest application platform and plan accordingly.