He's still a decent character, but the thing is that he's much better in Smash 4. He's got just as good of a combo game (if not better than in Smash 4), but it's harder to KO the opponent with him now. His up smash still KOs relatively early, but the range on it got way nerfed. F-smash is slightly stronger than in Smash 4 which is awesome; it's just not as fast as U-smash but it could still work. D-smash...yeah, it's workable but not impressive. Mario's SJP is stronger than in Smash 4, while his down aerial still KOs near the ceiling but the hits connect slightly less well but still work. Overall though, Mario has decent KO potential but it's still harder to KO in Ultimate than in Smash 4.
Ness...that's not the case. I can combo with him AND get KOs with him easily. Ness feels amazing to play, and he clicks with me very well. I'll still use Mario as a secondary, but after the nerfs I mentioned he's harder to play for sure. I still think he's a good character, but I wouldn't rate him as a top tier...I'd put him as an upper mid tier, bottom of high tier at best. Ness I think will be a solid high tier, on the other hand.