That video doesen't prove anything. Throughout it, I noticed many unfair reasons how he beat some of the level 9s...
Spamming moves (anytime which he plays Zelda, specifically against Game and Watch, where he used dtilt about 13 times)
Being lucky (Marth VS Peach is a prime example of this)
Using broken characters against lower tiered ones OR unfair matchups (Fox VS Bowser? Meta Knight VS Zelda, Marth VS Peach, King Dedede VS Kirby)
Chaingrabbing (Dedede VS Kirby, on Bridge of Eldin as well)
Using stage to advantage (Yep, you guessed it... The chaingrab in Dedede VS Kirby)
And most importantly...
HE USED ITEMS! (Fox VS Link, you can see a Bob-Omb drop from the sky, Smash Balls in Samus VS Samus and Link VS Link)
Also, I have a new list of what I consider the hardest Level 9 to the easiest if I use the same character as the opponent...
Pikachu
Wario
Diddy Kong
Mario
Luigi
Ness
Meta Knight
Lucario
Ice Climbers
Wolf
Pit
Kirby
Mr. Game and Watch (seems toned down in PAL version)
Fox
Marth
Zelda
R.O.B.
Falco
Peach
Toon Link
Sonic
Ivysaur
Yoshi
Snake
Donkey Kong
Jigglypuff
Sheik
Charizard
Pokemon Trainer (as a whole)
Samus
Link
Squirtle
Zamus
Ganondorf
King Dedede
Captain Falcon
Olimar
Bowser
Ike
And there you have it. I know it may be wrong to you, but it's MY ist.
NOTE: NOT A TIER LIST.
EDIT: LOL. I just realised I forgot Link.