What can Menus do that Taxonomy cannot? 'Comments', 'Users', 'Taxonomy' are Entity Types because they each define their own sets of required fields.

I am having a discussion with my boss where I am arguing that 'Menu' are really just a type of 'Taxonomy'. This is because Taxonomy has a parent field, and a title, but Menu also shares this, and extends it to require a 'link' field. He, however, disagrees with me and says that there are things which Menus can do that Taxonomy cannot. But I don't see what.


'Menu' has the concept of hierarchy, so does 'Taxonomy'.
'Menu' has a 'link' field to link to a Node, or an external link. But this can also be done using 'Taxonomy', by manually adding in a 'link' field manually.
You can control permissions on 'Menu' items, you can also do this with Taxonomy


I understand that a 'Menu' serves a special and common need, but conceptually I think it's just a type / superset of taxonomy, not another Entity. I think this chain of thought is common, as reflected by the number of sites that uses the Taxonomy Menu module.

In a previous question, I grok that Comments and Nodes are different Entities because they have completely different fields. But here, Menu seems to have the same fields as Taxonomy - namely parent and title.

So, why has the Drupal community decided that Menu need to be its own Entity Type, instead of a being just a module that extends taxonomy? (i.e. Taxonomy Menu) What does Menu offer that you cannot achieve in Taxonomy?
Basic difference I run into some time ago: a menu can link to only one content where taxonomy term can refer to several nodes. So, if you need a relationship node -> term that allows one node to be marked with many terms (and, in consequence, have one term assigned to many nodes) then menus won't do that for you (at least not out of the box). Node -> menu relationship is more 1-to-1 where node -> term is 1-to-many.