I think that the Tier system is actually broken as shit.
I've been able to take out Uber Pokémon with Pokémon Smogon places in the lower tiers (i.e. taking out a Xerneas with a Mawile – not even Mega-Evolved), and some of my Uber Pokémon have lost to "weaker" Pokémon as well.
There is no strong or weak Pokémon – the only thing that matters is how you train them.

You know, smogon isn't this raging, asshole kid that bans absolutely everything. They want fair games. They'd like you to use your favorite pokemon, but without getting bodied. They don't want bullshit or game breaking strategies.