There are some people who have been successful with low-tiers and won tournaments (like aMSa with Yoshi, Germ with Link, and Sethlon with Roy), but they won because they had a much higher skill level and knowledge of the game than the other attendees. Other than some specific MUs (for instance, Link and Marth go pretty even), the low-tiers are generally blown out of the water by the high-tiers.
Some may think I am being too generous with the balancing of Melee, but I think tiers 1-8 are really good, 9-13 can be pretty good in tournaments, 14-16 are on the brink of nonviable (but still on the viable side), 18 and 20 (I think Roy still has some potential, but Marth is always going to be better) are hanging on for dear life on the ledge of viability, 17, 19, and 21 are pretty bad, and everything below that is garbage. Keep in mind that is my opinion, though. In addition, I would like to say that Link and Young Link are extremely viable secondaries due to their hard counters against Peach.