No one is saying subclasses can't have different abilities and the like. The point is the core material of "How tough of a dude are you and how well do you hit people"? stay the same. In 2e it didn't matter if you were a fighter, a ranger, or a paladin you used the exact same hit die, THAC0 table, and saving throw table. For priests it didn't matter if you were a cleric or a druid you use the same spell progression table. Etc and so on. That's what's being done here. They are saving "Okay, so here's the empty shell, the skeleton of a class if you will that has the hit points, attack bonuses, and spells per day of Squishy Man With Mystical Powers". What type of Squishy Man With Mystical Powers you are depends on what subclass you play. The default subclass is Wizard but they've neatly portioned off what parts of the overall Wizard belong to the Squishy Man With Mystical Powers skeleton and which come from him being a wizard specifically. The spell selection, methods of casting, stuff like that all comes from being a wizard. This is how every edition except 3e has done things and they do it for a good reason. It gives future designers something to build off of, a base point to jump from. If you balance the skeleton with the rest of the game and the skeleton is 50% of the character that means you've balanced 50% of the game before you even add in the rest of the class. I don't see why this is such a point of contention.