Honestly, i'm always amused by how far people who don't play Nesses extensively want to air out their well defined theories on how well balanced he is. Even after you have me, Akhi, StereoKIDD, and Boiko all saying he's definitively low tier, that he seems deceptively good because he can handle fast fallers, people are STILL putting him in B tier. Statements like "Neutral game is the most important thing, and this character loses to dash dance" are relevant--until they are aired out about Ness's state in the game.
I can see why the facts can be obfuscated. Ness's flaws aren't obvious like fatty flaws (DK/Bowser), There are Ness's who have good bracket runs here and there where they engage and wreck fast fallers (Aki at WHOBO) and people who don't know wtf they are doing, and you have someone like Calabrel on the development team who doesn't compete, and feels fairly competent in his experience that Ness has a "middle tier neutral game that is underrated". But trust us when we tell you, Ness loses a large enough proportion of matchups and has some pretty bad matchups to ever justify him in his current state being better than the tier DK is in. A 6% magnet and a damage change so his fair is easier to SDI on the first two hits but worst to SDI on the last two hits is not going to change that. Character needs a few more fundamental strengths in his column to not be in bottom tier.
For the record, I feel Ness loses the following matchups badly (6-4 and worse):
Wario
Luigi
Zelda
Fox (when played with matchup knowledge)
Sheik
Link
Toon Link
Ivy
Samus
Pit (arrow cancelling pkthunder was murder in 3.02 and I believe it still is. I can be corrected on this one)
Kirby
DDD
Ike
Marth
Roy
GnW
And I think he loses the following matchups slightly:
Mario
Peach
DK (debatable--the grab range and kill confirms are crazy. Really easy for him to setup grabs on Ness)
Captain Falcon
Wolf
ICs (he's the perfect combo weight to be chaingrabbed inescapably for SoPo OR both of them
Mewtwo (? unsure on this one. Boiko could share more)
Lucario
ZSS
Olimar
Rob
Sonic
I think he goes pretty even with Squirtle, Charizard, Ganon and potentially Falco. I have no opinion on him v. Diddy, Lucas,and Metaknight since he has a pretty nasty punish game v fast fallers. Those might be even. He probably handedly beats Bowser, Jiggs, and potentially edges out Pikachu, as well as players playing any character without matchup experience. I don't know how he does v. Yoshi or Snake (this one might be slightly in Ness's advantage). I'm curious to see what Boiko and Aki think but this is how I feel the matchup spread of the character is.
I think it would take 3-4 minor tweaks though to give him a lot of 50/50 matchup spreads. Tweaks that Boiko and I have been talking about privately and are trying to test out.
EDIT:
Also Boiko, I really like your tier list. I'd push Wario up though to A tier. Beyond that, we have some personal disagreements but i can respect the positioning of everyone on it. I think Ganon and Yoshi are probably too low, but I admittedly know very little about how much Yoshi has dropped off. From what I can tell, Yoshi's still got a decent dash dance, bair, fair and his general non floaty + DJC combination theoretically still gives him a decent neutral game. His smash attacks/tilts are still decent, and he has a projectile that can force an approach so I have a hard time believing he has a really bad neutral. But who knows--I don't play that much with Yoshis. That's why I wanted to hear from more of them.