A wizard is as good at front line tanking as a fighter? A fighter is as good a healer as cleric?
I'm sorry, can you post again but starting from reality?
You give examples where you quote game mechanics (such as effects of spells (and by extension what classes have access to those spells) and call it story. It's not story, it's design and mechanics.
The decision of WHICH narrative identifiers are chosen to be represented in the game through game mechanics is due to the needs of the STORY. That's my point. The STORY says we need to identify a character's "strength". So the game designers come up with a number to represent that "strength". The STORY says we need to identify a character's "health". So the game designers come up with a number to represent it and call it "hit points". The STORY says that a character can choose to "wear" various type of "armor" and thus it makes it harder for that character to "get hurt". So the designers come up with a number to represent it and call it "armor class".
But none of these decisions are REQUIRED for the game to run. You don't NEED any of it. The designers could all have easily decided that characters could "wear" anything they wanted (chosen by the player), and that every character would still have the same "armor class" because they didn't feel the story of the game needed a difference in the math and mechanics to represent what characters were wearing. Just like in the game presently it does not give us any math and mechanics to decide how much any character gets to talk on their turn. The game certainly COULD. If they felt the narrative of the game needed to have each character only be able to say a certain amount of words in a turn, they could add in math or mechanics to represent it. But the designers decided that this part of the story in the game did not require mechanical representation.
And thus, anything in the game COULD be removed if the designers felt the math and mechanics were unnecessary to represent it. Why are there "wizards" and "fighters" and "clerics" and "rogues"? Because the designers had them in the story and narrative of the game and they felt they needed to be represented by math and mechanics. It's NOT because they had all this math and mechanics lying around and them saying "You know... the game has all these dice rolls we've put into it... maybe we should decide what they represent?"
So when I said above that "There's a fine line between ALL the classes in the game. And that line is purely story and fluff based."... it's because anything math and mechanics-related was inserted due entirely to what the designers felt the STORY needed representation for. That could be for almost anything and everything that appears in the narrative (3Eish "rules for every occasion") or almost nothing (if there's a question with what happens in the story, flip a coin to figure out who gets to decide). Why is a "wizard" worse at "tanking" than a "fighter"? Because the authors decided their story wanted that to happen and put in math and mechanics so that it would. But had they not cared about which one could "tank" better, they could have just not put the mechanics that would represent it. And the players themselves could have just decided in the story "this time, my wizard is going to be the tank for the group."