Since language isn't science, and since dictionaries are only meant to describe how people use words, not tell people how to use words, that claim could be made about any grammar rule or word definition or spelling, with some degree of justice.

The counterargument is that clear communications is helped along by adopting common conventions for word usage.

And the linked article only points out that there are ambiguous cases where less or fewer are equally appropriate, not that the rule has no merit.