Honestly, maybe other people have smaller top tiers than I do, but what is it that makes Lucario only high tier while characters like Mewtwo and Marth are accepted as top tier?
1) Buffs. A buff immediately calls attention to a character. If, say, Bowser had started the game with his current up throw, it would have been accepted as matter of fact by now. Kinda cheesy, but well-explored. Buffs (at least, significant ones) attach an X-factor to a character, where you know they've gotten better but rely purely on theory to figure out
how much better. I was going through 2014 CCI logs on a lark and it's very funny to see respectable posters talking about high/top tier Shulk and Ike after their 1.0.4 buffs. So people knew Marth/Mewtwo were capable of something better and were thus mentally prepared for any big jump. Lucario has received some changes, but hasn't received the kind of overhaul that would lead to shifting perceptions>
2) Results. Like, a really wide gulf of results between Lucario and Marth/Mewtwo. It's not as though Aba won Pound and then never did anything significant with the character again (and indeed, after Pound many were loathe to call Mewtwo a top tier.) Mewtwo took Aba from a kind of gimmicky threat who could occasionally challenge the best to a clear top 10 player and possible #1 in Japan. Players like Wadi and Rich Brown went from regional threats/relative unknowns to top 25 in the world. And Marth has spearheaded the rise of Pugwest, Mr. E, Fuwa, and of course Leo. They've put in a lot of work! Whereas Lucario has pretty good Japanese results and now 2nd place at an American major, with Tsu being the first ever Lucario to even crack top 8 at an international tournament. People have seen this before: they've seen Ranai, getting 2nd at Genesis 3 and then dropping off the face of the earth; they've seen Kameme, getting 2nd at EVO and failing to make top 8 in the US ever since. Can you really blame people for hedging their bets?
Marth/Mewtwo have obviously strong tools backed by a year of top tier results. Lucario has a far more obtuse toolkit and a good, if inconsistent regional/national record. That's the difference.
3-2 Shuton 
