There are a lot of Snakes Samo, and he doesn't win every tournament ever (see also: Metaknight). He's good, but not unstoppable. Think of him as Brawl's version of Fox or Falco.
In fact, the competitive balance of Brawl compared to Melee makes some more sense if you draw allegories between Brawl characters and their Melee counterparts. This is comparing the 2006-2008 Melee tierlist Top-Middle tier and general character sentiments in Brawl (with some help from Ankoku's Character Ranking list). My Melee metagame knowledge is a tad rusty, so if someone in the know could back me up/clarify things, that would be great.
Snake = Fox: Great projectile game and many tricks up his sleeve in close combat. Has somewhat of a learning curve, but is hands down one of the best characters in the game.
Meta = Shiek: An incredibly quick ball of priority and **** that can rack up damage to an insane degree. One of the best as well, just like Shiek in the olden days.
R.O.B = Peach: Great air game and annoying projectiles, coupled with a steep learning curve and general degree of WTF. In a class by himself really, not quite **** tier, not quite general High tier.
Falco = Falco: The more defensively minded Spacie, able to play good keep away until an opening for big rewards open up. Slept on in the beginning as well, but with enough jank for an ascension to his old spot to be plausible.
G&W = Captain Falcon: Mad rushdown abilities and air control making for a combo-happy character. ZSS is basically Melee Falcon with **** and some range to her as well.
DeDeDe = Samus: Floaty bruiser who's hard to use and harder to kill. Good at spacing and adept in the air. Lucario might fight this designation as well.
Wolf = Dr. Mario: A powerful character who's game is built around a versatile projectile, but is hosed off of the stage. Has to be played smart and defensive against the higher echelons.
Wario = Jigglypuff: Quirky character that has advantage over someone higher up in ranking, with arguably the best air game around.
Marth = Marth: The second character that the nerfbat missed, still got range, comboability, great air, pretty much everything that made him good in Melee is back in slightly different fashion.
Donkey Kong = Ganondorf: Big nasty mofo who is nimble in air and hits like a bus full of fat people. Might have advantage over higher ranked characters, might not.
Pikachu = Mario: The sleeper hit. A surprising entry who might not be quite as good as his peers, but is still a contender. Makes his bones with combos and general speed.
Pit = Ice Climbers: This one's a bit of a stretch, he's got some good parts, several helpful ATs, and noobs who face a good one cry "broken". Hasn't had that one player push him over the top yet, but is considered a strong choice. If people outside Corner-Trap and Void play ICs, they might get their spot back.
Toon Link = Link+: A good character with many projectile tricks and general ability that has not done well for whatever reason. The potential is there, but it's just not been tapped yet. Diddy Kong is in this boat as well, he's seen to be good but just can't get it done at this point.
Sonic = Donkey Kong: A character that nobody is really sure as to their ability level. When he's considered good, he gets stomped; when he's bad, Lucky wins a tournament. A character with good and bad in equal measure and possibly the hardest viable character to use.
Also lol@Captain Falcon being Dan Hibiki. The sad thing is that it's more or less true, and this is coming from a dedicated Falcon main. He's like Melee Game and Watch, to keep the allegories going.