Merriam-Webster is one source of definitions for words. They aren't the ultimate authority. It's not like their dictionary is written by God.

In this case, they didn't get their definition right. What they had disagreed with the definition in medical textbooks, etc.

The correct response, if any response is warranted at all, is to blame Merriam-Webster for putting an incorrect definition in their dictionary. Not to start drawing invalid conclusions based on incorrect definitions.