When fighter and rogue are defined by what they do (fight and steal, more or less), and cleric and wizard are defined by how they do things (Use Magic), the names really don't actually tell you that much at all. Someone with a heavy LotR mindset (not unexpected, given the popularity of the movies) will probably expect Fighters to be pretty damn awesome, and there's a very good chance they'll be disappointed to see Wizards capable of completely overshadowing them over and over again, except and unless there are big fat sacks of HP with some Legendary Saves to slowly whittle down to 0.
These words do not actually tell us as much as you claim they do.
How do you mean? I see "calling a fighter a defender" as in no way whatsoever different from saying "fighters have good defenses and can interpose between their allies and the threats they face." Where is this conflicting with "the game as it is intended to be played," and what exactly IS "the game as it is intended to be played"? Because that sounds to me like a fancy way of saying, "The word 'defender' is badwrongfun."
Well, that's nice, but you're abusing the different senses of the word "role." 4e consistently uses "role" in one way: the answer to the question, "What functions should this class be consistently competent at in combat?" The 4e term says nothing about anything that isn't combat, because that's a separate consideration; this is not to say that classes therefore lack things outside of combat, merely that 4e doesn't have a term, description, or specifically-declared mechanical goal for things outside of combat.
You're using the word "role" to answer the question, "What functions does my character contribute over the course of its entire life?" This question is fundamentally different, and I'd argue it's beyond the scope of being answered in the way that 4e answered its "functions in combat" question. Your question admits so many possible variants and is so deeply dependent on the context of each table that I don't believe it can be answered systematically.
"Wizard" is what you contribute to your player-group, sure. But that's not, at all, the same kind of "role" that 4e talks about. Conflating the two is at best just confusing, and probably more like strawmanning.
Ah, yes, the "truth" that class literally doesn't matter and you can do absolutely anything you want...except that that hasn't been true since at least 2e and probably earlier. The Fighter was always--even from the 0e days--intended to be a meatshield and to tell people "you shall not pass" with a weapon to the face/body/etc. The whole "marching order" thing and the like. That's the design of the class. People can take the class and then actively oppose what it's designed to do, but that's probably an exercise in heartache. The only way to not do that is to have a class designed to do absolutely everything...at which point "class" really doesn't mean anything anymore.