Well, I think, and IMO and all that, that the more lore that is built into a concept, the less it becomes a class and the more it becomes an archetype. If you look at most of the classes, before they choose an archetype, they really don't have an awful lot of lore built in. There's some - a cleric is a holy dude or dudette, a barbarian comes from the outskirts of civilization (typically) but, you could take any of the classes in radically different directions based on the archetype.
That's why you see fairly serious and pretty well supported arguments that some classes might be better served as an archetype. If paladins were limited to the LG paladin of earlier editions, then, really, they'd be an archetype with an alignment restriction. Why waste an entire class on such a limited concept?
It's one of the strengths of 5e that they use the base class and then branch off with archetypes. It makes the game simpler, for one, in that you don't have thirty different classes in the game, many of which are just variations on a theme. I mean, not to pick on
@LuisCarlos17f, but, ninja and samurai are archetypes, not classes. A class needs to be a bare bones chasis that you can bolt archetypes onto.
What can you do with a Samurai class? It's so limited that you can't really build archetypes off of the base concept. Same with ninja. 5e HAS ninjas - a couple of them - Assassin Rogue, Shadow Monk, and I'm sure I could build a decent ninja using a warlock as well.
It's a really interesting concept that is found pretty much only in 5e. It might have some ancestry in Prestige Classes in 3e, but, not really. 5e has build in the notion that before 3rd level (most of the time) you're not really anything. You don't really get into your "class" as such until you get your archetype.