I don't know if you're misunderstanding me or something, because I feel like this is going in circles, but I'm not arguing with the importance of mastering fundamentals. Those come into play before any ATs or any tricks your character has.
But that doesn't just equalize differences between characters, the ATs and other tools available to your character change how match ups play out and change the potential of that character. Even if you can beat MK, it doesn't change the fact that the tools available to MK are better than the tools available to Lucas. Obviously, if the MK doesn't have a mastery of the fundamentals, he probably won't win.
But since the match ups, the metagame, and all the things that matter when considering what makes a character "good" should all be determined on the highest level of play, we should assume that the players both have an equal mastery of the basics. This game doesn't rely solely on player skill, certain characters can just do things better than others.
I don't remember seeing anyone in this thread arguing that "bad" characters couldn't compete at high levels or beat characters that are better than them, the only thing I've been trying to say is that Lucas isn't a good character, and you're trying to refute that by saying that you're a very good player. That doesn't make any sense.