While Melee is far from perfect, so far out of all the people left, we have the following characters as main characters or prominently used characters by people who are still alive in EVO in Melee:
-Fox, Falco, Sheik, Marth, Captain Falcon, Jigglypuff, and Peach players galore (7 characters).
-Quite a few Ganondorf, Dr. Mario, Samus, Young Link, Ice Climber players, including my pal Chok!!! (5 characters).
-A select few Mario, Luigi, Pikachu, Donkey Kong, and Zelda player(s) left. (5 characters).
That is at least 17 of the 26 characters, if not 18 or more characters, being represented in the quarter-finals. That's a pretty good margin. Considering 2 characters are vastly inferior to similar characters (Roy to Marth, Pichu to Pikachu), 17 out of 24 is pretty good of characters left.
That is also not counting players who have played other characters in tournaments recently (ie: Taj, who plays Marth and Mewtwo who made), but only characters that will definitely be pulled out.
Heck, that one super good G&W might still be left, Bowser if Gimpyfish survived somehow, one of the few Link players who possibly snuck in, one of the few Yoshi players who may have survived, and Taj, who as previously mentioned could pull out Mewtwo in the right situation.
Also, today on the streams I literally saw every character... minus Mewtwo, Mr. Game & Watch, Pichu, Kirby, and Link, and I know for a fact at least one person played Mr. Game & Watch for legit and several people played Link.
So that means literally every character but 3 maximum weren't played (Pichu, Kirby, and Mewtwo, aka the bottom tier).