Literally the only reason that Captain Falcon isn't the best character in the game is that some characters are too good in disadvantage. Falcon has a combination of the 2nd best advantaged state (the only better advantage is Fox, because of jab cancels, hello 2 frame move that sets up into KOs/30% damage, what even is that) and one of the best neutral games in the cast, probably 3rd or 4th best (Sheik and Fox are better, Rosalina+Luma is a close call).
Falcon in neutral is fierce and safe; he does not care about zoning because of his speed, he does not care about shield because of his dashgrab, he does not care about pressure because of jab, and he has mixups bulging out of his muscles. You can fastfall jab or turn around jab and beat most options that the cast has, but you can also falling up-air, b-air, crossup in one of a dozen+ ways, d-tilt, n-air, empty hop... Falcon's options go on and on. And the coverage on his aerials is mad strong, b-air and up-air and n-air combined create a mini death star of traps that do way too much damage overall. His bad disadvantaged state and recovery do not make up for his neutral and advantage against many members of the cast, even if he has even matchups such as vs. Yoshi. 14% off of a totally safe b-air that can be combo'd into at kill percents against light characters? Absurd.
The reason that Falcon doesn't break the game in half is that Pikachu, Sheik, and Zero Suit Samus get out of disadvantage for free. The risk:reward ratio for these three characters (who can all edgeguard Falcon to some extent already) is distorted in their favor. If Pikachu did not have Quick Attack to get out of disadvantage then Falcon would be one of his hardest matchups, even with the edgeguard; onstage b-airs and jab shut Pikachu down pretty hard, it's just that Falcon can't follow up too well on him. I always lose neutral to great Falcons who aren't afraid of Pikachu's height pretty hard but still win overall just because I do 30-40% per string while Falcon only gets in one meaty 14% hit and is done, because Quick Attack is too good in disadvantage. And while Falcon's edgeguarding game is really strong, these characters just flat out do not care about it while edgeguarding him back.
This game is not fundamentally balanced. The top 20% of the cast phenomenally outperforms the remaining 80% in advantage, disadvantage, and neutral. Pikachu, Sheik, and Zero Suit Samus vastly outescape everyone in disadvantage, for example: Bouncing Fish, Flip Jump, and Quick Attack are the best moves in the game for that reason. Think about this. Literally almost the entire cast does not like to be offstage or in the air getting juggled, but these three characters often manage to treat it like it's neutral. Landing is too easy for them.
You have characters who are grossly overpowered in advantage (Ness, Luigi, Falcon, ZSS), and characters who are grossly overpowered in disadvantage (Pika, Sheik, ZSS), and then when you add in ridiculous neutral games due to Needles or Fireballs or Falcon's dashgrab (or in ZSS' case just advantage+disadvantage), they invalidate most of the lower tiers.
Character balance is good, better than it's ever been, but what Reflex says is absolutely true: the top tiers are playing a different game.