I just hope you guys all remember tiers aren't static.
Even if, theoretically, a game was 100% perfectly balanced(which isn't possible, btw), there are still other factors that can contribute to tier list. Namely, how developed their metagame. A character could have a ton of potential, but a skilled player has to take the time to notice and unlock it. If you think your main isn't at the spot on the tier list it deserves to be, then focus on getting better so you can show other player that they don't suck. Of course, I'm a pretty mediocre player myself, so it's not like I'll be making any changes in Mewtwo's or Charizards metagames any time soon, but I can at least say good things about them to hopefully attract new players.
And of course, there's also more then one way to make tier list. Just look at competitive Pokemon, where tier list are based entirely on usage. It's more of a guide to tell you which threats are relevant then to tell you which Pokemon are "good". There's also tier restricted battles to give obscure Pokemon more relevance. Now, I'm not predicting that Smash is going to adopt this policy or that it ever should, but it helps prove extra perspective of what a tier really is. Everyone's view of the character is just as important as the character itself.
Pokemon tier list are also incredibly dynamic. If one Pokemon becomes popular, Pokemon that effectively deal with it will become more popular in return. This is, to a lesser extant, true to Smash as well. A character's match up against the other high tiers is incredibly important. It's not nearly to the same extreme, as swapping a Pokemon team is much easier than swapping a Smash main, but it still happens.