Responding to the original post, before my thoughts get swayed by the 10 pages of replies.
I think "Fighting Pet Owner", be it an animal companion, undead henchman, steel defender, holy mount, dragon mama, or whatever, should be a unified mechanic to be used by multiple classes.
So I don't think that should be owned by the ranger.  Should the ranger have access to it?  Sure.  But, if it's not a signature of the ranger, I don't think all rangers should be required to take it.  Many archetypes of the outdoorsman don't have such a companion.  And some, like the Beastmaster (book or film, even though they are very different) have multiples, not all of who are combat-focused.