The Fighter, Rogue, and Sorcerer are the three "generic" classes as far as flavor are concerned. They don't have individual narratives for what kind of person they are... that comes out of their subclasses. But why does that actually matter? Why does it matter where their unique "identity" comes from? Now sure, one could make a dozen "new" classes that are merely the subclass identity given a larger Heading in the Classes chapter in the book... but does that necessarily gain one anything? So we have a Thief class, a Samurai class, a Storm Sorcerer, a Swashbuckler, Cavalier, Draconic Sorcerer etc. etc. and the "Fighter", "Rogue", and "Sorcerer" no longer exist. Okay. Our "Class List" is now bigger even though all the concepts are actually the same.If half the power and most of the flavor are in the subclass and not the class.. the class doesn't matter and the subclass should be the class.
So what's actually been gained? Anything? I personally don't see it. Now I'm sure one might argue that making these things now true "Classes" would probably imply that the designers would most likely make new and different mechanics for these "classes" to make them more unique... and "new mechanics" are always good for a certain subset of the gaming populace who want new mechanics all the time. But that's not actually guaranteed, plus there would be an equal subset of players annoyed by all of at that. After all.. we still have that group of players out there still whining that the Ranger and Paladin are still classes and that what they truly want are just the Core Four with everything else subclasses for whatever reason.
So making changes like this does not ultimately solve anything. Some would love the changes, some would hate it. And NO ONE can claim that their side of the issue is objectively "correct".