Regarding results: Ness had fairly good results in Smash 4 as well (18th best near the end, ROB 19th best), yet both were considered mid tiers back then (see:
https://smashboards.com/threads/tournament-placing-database-scoring-project.437773/). Mega Man, a high-mid tier, got the 16th best results at that time. This shows that good results do not necessarily mean that a character is high tier. Ness was overrated for a long time in Smash 4 and he might be in Ultimate as well, time will likely tell.
On the latest official list, Ness was at the bottom of C tier, #28th in the game. #28th isn't that close to high tier. I think he might be a bit better in this game (relative to the cast) but I'm still skeptical of him being high tier. Players like FOW and Shaky and Awestin are very good though, and Ness might be at the top of high-mid even (which makes this discussion somewhat silly I guess, since the difference between the top of high-mid and the bottom of high tier isn't exactly huge).
Mid-mid at best, probably low-mid. As far as I know, he still has most of his Smash 4 flaws, and his up-Smash hitbox is worse. Keitaro does not seem to have much faith in him, and I think AC (now Armando) dropped him? Actually, I looked it up and he posted this a few hours ago:
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It'll be interesting to see what he can do with Falco.
Ness probably loses to swords, right? And many people seem to think Pichu also struggles with swords, so Inkling might be the better choice (though it's possible Inkling, too, struggles with swords, I haven't looked into Inkling's matchups as much as Pichu's).