I decided to look at the character diversity in Brawl in a different way (actually, I was just trying to prove someone on Gamefaqs wrong and ended up coming up with something too smart to only post there).
The following characters have placed top 8 in a tournament with 90+ entrees since the start of 2009. 90 entrees is my cutoff for a major tournament, and I decided at that number BEFORE looking at the list (so it wasn't picked to specifically maximize what I'd see). The highest place is indicated in parenthesis. If their placement on the list is only due to a split, it will be indicated with an asterisk.
Lucario (1), Snake (1), Meta Knight (1), King Dedede (1), Diddy Kong (1), Mr. Game & Watch (1), Zero Suit Samus (1), Wario (2/1*), Pikachu (2), Falco (2), Luigi (2), R.O.B. (3), Lucas (4/3*), Sonic (4), Donkey Kong (4), Samus (4), Marth (5/1*), Pit (5/4*), Toon Link (5), Ness (5), Kirby (7), Ice Climbers (1)*, Peach (3)*, Zelda & Sheik (3)*, Pokemon Trainer (3)*, Wolf (5)*, Fox (7)*
That is, 7 different characters have won major tournaments by themselves, 21 different characters have placed top 8 at major tournaments by themselves, 10 characters have won major tournaments if you allow secondaries alongside them, and 27 characters have placed top 8 at major tournaments if you allow secondaries alongside them.
The tournament "Road to Viridian City" would have perhaps added more diversity (I didn't look at it after I was done), but it barely missed the 90 mark (it had 89 entrees). NO KOAST was similarly excluded (with 87 entrees). We could also point out that this only includes tournaments in Ankoku's stats so it's possible that major Japanese tournaments would have expanded this even more.
If Meta Knight is killing character diversity in Brawl, I am not seeing it.