Ness in my opinion is still a top 20 character. Yeah his recovery is simple to gimp, his neutral is meh and he has trouble getting in often but once he does your taking a lot of damage fast.
We all know about his Dthrow strings but he also can get good damage off falling Up-air which is safe when spaced properly. Up-air at zero will lead into a grab. At low percents up air can lead to up tilt which you can follow up with a Neutral, Up, Foward or Back air. I've been able to connect a PK fire after a Bair but I don't know how true this is. PKT is great for juggles and adding damage against characters that don't land well. Should you land it PK Fire of course deals great damage depending on what the opponent tries you can follow up accordingly (SDI up and away and jump out you can Fair, SDI back or roll out you can just chase them and grab anyways, try to jab you through it as you approach throw another PK Fire)
Ness is also a excellent ledge guarder with off stage PK Fire trapping people who try to jump back from the ledge which can lead to a Dair or Fsmash kill. His PK Thunder tail can gimp and force opponents to recover how he wants. His Down Smash is excellent at catching 2-Frames and it makes the Cloud and Rosalina MU's SO much less irritating. And should he leave the stage and edge guard his strong aerials, long lasting Nair and Fair can knock people far back and kill.
He just has so much kill power. Uair, Nair, Fsmash, Dsmash, Bair, Back throw, Foward Throw (Situational), PKT, PKT2 he can kill you and get you to kill percentages quickly. For those reasons alone I can't see him outside of top 20. I wish FOW and Shaky would travel more, NAKAT doesn't use him as much and other Ness' like Awestin, Ribs and S1-14 are more regional threats rather national.