Let's put it this way. You claim you're not reducing archetypes. Okay.

I create a class that gets full casting, knows every spell printed, had Extra Attack and additional Extra Attacks at every level the Fighter gets them, gets Fighter ASIs, and gets one subclass from every class in the game.

You can, of course, choose not to use most of those features! You can play your "I only wield arcane magic from the wizard list out of my spellbook" wizard despite being of this class! But all the options are still there, if ever you choose to take them, and refusing to use them is your character in character choosing not to do things he's perfectly capable of doing.

As opposed to your character actually only having the powers of a wizard.