Last I checked, no-one used Warcraft as a measure of what is "real" anyway. Given that the term Paladin has been around since at least 8th Century Frankia, I'm fairly sure that the Paladin in Warcraft is an abortion to what Charlemagne's greatest considered.

Also, the classes are a bag of mechanics, and use internalised names to make rules reference easier. A Paladin of Devotion isn't a Paladin of Devotion, she's Aaliyah the Healer, Apprentice Sister of the Order of the White Rose, while the Oathbreaker is Krios the Reaver. A Fighter isn't a Fighter - they are Dave the Barman. A Druid isn't a Druid, they are Kath'gor, Arch-Shaman of the Snow Leopard Tribe. A Monk isn't a Monk, they are Sensei Miyagi. A wizard doesn't cast Fireball. The cast "Conflagration of Har Ganeth". A Sorcerer doesn't cast Fireball; they don't even cast Conflagration of Har Ganeth; they simply cast raw magic that appears in the form of a fireball. My Hexblade doesn't call the Curse Bringer Greatsword, he calls "Harvester", a great Scythe.

I care little about what some dude in an office believes is how something should be run. It's a roleplaying game, and the dude in the office on the other side of the world isn't playing the role, I am. Or the player of the Paladin is. The mechanics represent their abilities in game, not the name dreamed up to flavour some abilities.

I don't have a problem with someone pulling the abilities of the class and its fluff wholesale if that's how they're roleplaying. They can call themselves a Paladin of Vengeance if they want.

As to your complaint of what a Vengeance Paladin considers the Greater Good, here you've got the same issue - say that a Party containing both a Devotion Pally and a Vengeance Pally get the same individual that the entire world will be destroyed if a child is born to X tribe of Barbarian Orcs? What greater good is there in the possible genocide of the entire world, if you allow that tribe to live?

Say you're given a child to hold, and you get a vision telling you that if this child reaches adulthood it will bring about the holocaust; it's Hitler, or Pol Pot, or Lenin, or Mao, or Margaret Thatcher, or Donald Trump or whatever individual who causes such damage to the world. Are you trying to suggest that a Devotion Paladin is going to allow that to happen, while a Vengeance Paladin would go all Gregor Clegane on the child?