I didn't say you can only be defeated by someone who does. Why are you caring about tiers? You use Meta Knight, but you get whupped by a Yoshi user frequently? One who doesn't use advanced techniques seen at world-level tournaments?
Most everything I've got to say about tiers and whether or not any particular person should care about them:You're not at the pro level. You're a casual player like me. You use Meta Knight because you like him, I know--and that is beyond okay with me. But since he is at the top of Brawl's tier list I'll use him as an example. Hypothetically, he could be the worst character in the game if you don't take advanced techniques into account, if his smashes and specials were bad enough. He could be a dead man walking in any match with items or more than two players. I know he has some broken moves anyone can use, but he has flaws, some of which only come into play with items and multiple foes. His Final Smash isn't the best, either, being pretty easy to dodge (as many are). Meanwhile, last-place Ganondorf has a great Final Smash that has a huge range and death power.
But see, that's not what the tier list looks at. Fox wasn't at the top of Melee's for his smashes or specials alone, but for his reflector and wavedashing and L-canceling and everything all put together. You don't see a lot of that in casual matches, do you? So for people like us, his placement at the top is irrelevant! Even if you're in a one-on-one no-items legal-stage match and you're at the same skill level as your opponent, the typical matchup could be meaningless because the aforementioned skill level doesn't bother with much more than reflexes and timing of attacks.
only high-tier characters, like Snake (or characters that "counter" high-tier characters, like Wario -> Snake) are ever picked by players
Untrue. Regardless of whether pros choose a favorite based on their moveset or who the character is, they play as their favorites. The tier list changes when players of lower-tiered characters learn more about using them effectively and their unique techniques become more widely used, aiding their results in tournaments, and bumping them up. It happened for the Ice Climbers in Melee.
People who obey the tier list are typically not really pros, just trying to impress you by not using characters who suck (like all your favorites, Sam, they all suck), not playing on any stage but Final Destination (which despite information I didn't read is unanimously fair and the only tournament-legal stage), and never playing with items (because even four-player party-style battles MUST be tests of skill. And not skill with item usage). I don't know why they do that. Being a total jerk doesn't impress me. Don't get me wrong, I'm not against tournament-style play--but I wish people would at least do it right and not treat players who play under rules designed for entertainment like garbage.
Tier lists kind of interest me, though they don't affect my game at all. My favorite characters (chosen for who they are outside of SSB) are scattered all over it. I want to see multiple tier lists for Brawl arise. One for the game unaltered, one for Brawl+ (formerly known as Melee 2.0, but it has had honorable changes made such as buffing lower-tiered characters in a never-ending attempt to balance the game. Perhaps I'll look into getting that), one taking all of Red's Pokémon as individuals as well as Red as he normally is (there are codes that let you play as one alone like in Classic Mode and I like 'em), stuff like that.
Just to remind you, I'm not claiming to be a pro. I've just done my homework and understand how the tiers work. It's not an attempt to steer people away from Link and Ganondorf, and if you look at it this way, it's not even a statement of who is better. It's a table of statistics of tournament results. The most logical reason to care about such data is if you'd be proud to main characters who are renowned to perform well (inversely, if your main is ranked low and you wish to improve their performance at the top) or you prefer to be stealthily good with a lower-tier character to throw guards off.