Ness has a ranged advantage. Ness can attack or spike rob out of his Up b, Ness' yo yo can punish Rob's spot dodge to down smash stuff. Pk thunder juggle...
Ness does not have a ranged advantage. Ness can't do anything to ROB at a range without getting hit with something. Rob can't just laser/gyro because of the Magnet, but that doesn't mean Ness has a ranged advantage.
You won't spike a competent ROB out of his up-b. I guarantee it.
You can punish ROB's spot dodge with your fair, too. But the thing is that spotdodge->dsmash isn't the only thing we do. It just so happens that those particular moves are extremely efficient for dealing with lower level play.
PK thunder is too slow to effectly juggle ROB. You'd need a faster projectile (like a Meta Knight) to seriously juggle ROB. ROB can fly, like, way off the stage and then recover. But then again I could be thinking of something else for PKT juggle, so please correct me if there's something else here.
PKF ***** the heavies... I got more but... What does Rob have. (and don't say CG)
With proper SDI I never had a problem with PKF =\
ROB has excellent range on the ground (and maybe enough in the air to challenge that beastly fair), a great edgeguarding/gimping game, projectiles to mix things up, and the ability to friggin fly.
Of course this is all just on paper, but some if not most of this stuff is going to translate well into real play.
I do hope I'm not coming off as condescending here, so please correct me if you think my views are flawed. After all, that's the point of these forums, right?