I know Link is a lot more common in Europe and pulls in results here quite commonly, but I am unsure how he fairs elsewhere. In a similar vein, Mewtwo is extremely uncommon, and almost unspoken of in Europe.
Off topic a moment (as a general thing, I'm not putting words into your mouth), I do want to say it makes me laugh when people try to say "X character is shouldn't be too high because they only place well in Y region". I'm not being funny, but we are all on the same planet, we're all playing the same game. Results are results, regardless of where you are. It's not like Melee where matchups and stuff differ depending on region; we're all playing the same patch. If a character gets results in Europe, you shouldn't discount them because you don't live there etc.
Nothing Mewtwo has done has ever been as "major" or noteworthy as Pound. All the other tournaments are noteworthy, but not Pound level. So what Routa alludes to is true; if say Link, was to win something huge such as Pound like Mewtwo, while he has lots of good results, I'd want to see him do it on a constant basis before we put him up there.
I know there are others that share this belief. I don't think there is anyone out there who thinks Mewtwo is lower than where he is now. It's not like we're saying "oh, he's a low tier character, I want more proof before we put him up there". I can see he's good, which is why he's up there, but for him to be amongst the likes of Meta Knight, Fox, Mario, Sonic etc, all characters that get high results on a constant basis, I want to see Mewtwo get high results on a constant basis also. Yes, I get he's won Pound, but like others have mentioned, lack of the best player, potential lack of matchup knowledge etc could have all attributed to this. If he starts getting constant high results, we know that it really isn't lack of matchup knowledge or stuff like that, and he deserves to be up in tier 2.