Ness loses to Sonic, both in theory where he struggles in mid-range / neutral in general and in results where S1 notably lost to Ixis at Albion.
But he doesn't lose to most of the characters presented because his damage per hit is silly high, and trades vs 80% of the cast work out in Ness' favour (Uair vs people that aren't Ryu or Ike trades well against most sex kick Nairs if it doesn't out-right beat them). The offstage argument is a difficult one because:
A) The opponent has to get them there in the first place
and
B) Nothing is guaranteed even should they be there
(Thanks Scoot)
With Ness it's a particularly difficult one to account for because he carries one of the best DJs in the game as well as an AD who's vulnerability frames are half inside the Z-axis. Good Ness players SHOULD be making it back without using PKT the vast majority of the time, they are specifically anti edge-guarding tools and are used as such.
If two players are playing a match-up who are evenly skilled, and Ness is winning the neutral about as much as G&W is, there's really no telling who's winning or not, because G&W might have gotten Ness off-stage and killed him, or Ness might have gotten a Dthrow Fair combo, a Uair chain and a Dsmash at the ledge to kill because G&W is volatile in a different way - weight. In this MU the character with higher percent is going to be forced to approach, and that comes down to whoever tagged their hits in early. In terms of neutral it's been a long time since I've versed a good G&W as Ness but
@Kofu might be able to shed some light on how that looks.
Most of these MUs that are being touted as losing aren't actually roadblocks for top all the way down to high-mid level players. After the discussion we had some time ago where most of these MUs just don't have a lot of evidence to work with, it's kinda been clear to me that no concessions have been made and it kinda just looks like you two are circlejerking a particular bias. You literally touted Pikachu as being a top 15 character with the top 8 results ESAM has made and then turned around and discredited the exact same achievements made by FOW and Shaky (which are actually a heck of a lot better). If you want to talk results Ness consistently pulls in around Sonic's level of results on Das Koopa's rankings, which is significantly better than Pikachu OR Villager. If you want to talk MUs, Sheik isn't like versing Brawl Marth and she's infinitely better than Rosa.
Oh, speaking of Rosa, the reason Ness ACTUALLY loses that MU is because as Mr_T correctly mentioned, Ness struggles to kill Luma reliably and safely. He can't deal with Rosa onstage while that little brat is running around, and he can't deal with aforementioned brat without risking hard punishes. This situation leads to Ness being offstage more than he is in any other MU which makes the gimp more likely. Ness poops on Rosalina in the reverse situation and any time you see a Rosa recover to the ledge in that MU you should be thinking "The Ness missed out on a stock". Dsmash catches Rosa
every time without exception should she recover to the ledge.
I'm ranting, but it bothers me because you keep telling me I don't acknowledge Ness' true weaknesses and the cite his offstage gimpability in every other MU. Ness is average in terms of safety in neutral / doesn't have real pokes, he doesn't like being juggled and he doesn't like being offstage. In return he gives that weakness to most characters he's versing (most characters actually can't deal with PKT juggles or tail gimping offstage) and has high damage per hit as well as several easy ways to close out stocks, a potent OoS option, ledge coverage option, punishes landings well and generally good frame data. He's not a particularly deep character, but he's pretty good.
But W/e if you want to rate Villager and Pika above him, go ahead, but as time goes on I assure you you're going to lose the justifications for keeping those two characters in top 15.
EDIT: Super grats to Nicko though. :D