Mewtwo + lucario =/= Mewtwo
X + Y =/= X
The two combined together as one entity (that entity being that which fulfills the niche) is a different thing altogether. You can replace one thing with a different thing, even if one of the additives to that "different thing" is the same thing. If I hand you a pile of sugar, then take away that pile of sugar and sand, are you going to say your sugar wasn't replaced? If not, then why not go ahead and still sprinkle it on your wheaties? You presumably will not, because sugar alone and sugar mixed with sand are simply different things.
If Mewtwo alone is X, Lucario alone is Z, and both is Y, then X was replaced by Y, and Y was replaced by Z. Mewtwo's niche was eventually passed along to Lucario. The only difference is, the middle-man of "Y, both of them," doesn't exist in game releases, because Smash went form one game with Mewtwo, to one game with Lucario.
Mewtwo alone and Mewtwo with Lucario are separate entities.
Are you kidding me? Mewtwo is Mewtwo whether by being with Lucario or not, adding Lucario doesn't make Mewtwo any different so Mewtwo can't replace himself. They are not separate entities because they involve the same person.
Really, this is making a mountain out of a molehill. If I gave you an Orange, took it away and gave you the same Orange with an Apple, is the Orange any different?
Not sure what you're trying to say. "We can mislead people to make them think they're completely different" isn't exactly a rebuttal. That doesn't solve the problem of them not being different enough.
No, your point was that what the masses initially sees is what is true, that has never been the case on its own. Being supported by the masses doesn't make it right.
I don't think both should have been in Brawl. Multiple characters fulfilling the same niche is a waste of space. I just have a feeling like Smash is going to rotate Fire Emblem characters and Pokemon. I'd have argued for "whatever generation 6's "special/movie pokemon turns out to be" a year and a half ago. It just happens to be that Mewtwo is getting special treatment, so I guess we rotate him back in.
Personal opinion has no jurisdiction on what happens in game, even if there were specific "niches," Smash has proven time and time again that they don't care and will use the same "niche." Lucas and Ness proved that, so even playing into your logic, that is not a good reason for Lucario to miss being in the game alongside Mewtwo.
No, characters were only cut once, you can't make a pattern out of one instance. There is no reason to believe that Lucario would be intentionally kicked out of the game instead of being alongside Mewtwo.
"Aura" and "psychic" are both "energy/magic." It's both using something that's immaterial-but-not. This would be on par with saying that if Luigi shot ice balls, he'd be a "different concept" from Mario because it's ice, not fire, when really, it's still just shooting an "element ball."
Not at all, Aura was used in a completely different manner then psychic abilities. Aura was used as basically a boost, making Lucario's damage output stronger or weaker depending on the situation, the Psychic abilities were used mostly as actual moves.
Second jump is undoubtedly a similarity, and there up-B is drastically similar. It's also very similar with Pikachu and Wolf, yes, but it's not unique like comparing Mario and Peach's recoveries, also same franchise characters.
No it is not, Lucario doesn't wrap like Mewtwo does nor does it carry any other notable similarity to it. It doesn't even have Lucario disappear in space. Again, you're trying to force this connection that was never there to begin with.