Well, no.
In 64, most everyone on the cast is viable. Ness's recovery is exploitable and his range is nonexistent. But he has a threatening combo game with his dair finisher, good mobility options with his DJC and the Nesslevator, and some excellent shield break and pressure options. So he's not great compared to the rest of the cast, but the entire cast is pretty viable.
In Melee, Ness was one of the flat-out worst in the entire game (ahead of Bowser, Pichu, and Kirby). His flaws are really, REALLY apparent when you play him in that game. His lack of approach, sluggishness, nonexistent recovery, subpar frame data, underwhelming moves, and even the lack of ability to perform rising aerials hurt. Do not misunderstand; in Melee, he was bad bad bad.
In Brawl, Ness had some good points, but the ability that some very commonly used characters had to get guaranteed followups on him out of any grab and also do straight zero-deaths in some cases, combined with how generally overwhelming the best and oft-used characters in that game were, really held him back.
In Smash 4, he's benefited from a changed engine and changed effects on his PSI-based attacks (which allows for some of his good combos), and subtle buffs to his recovery as well as universal changes to his kill options that make them much more viable. Plus all of the crazy buffs that PKT1 received, which make it a ridiculously good move. He's generally a little quicker, a little slipperier, hits a bit harder, and is much, MUCH better at killing (which was always his strength to begin with). He still has the old weaknesses (poor neutral, bad approach, exploitable recovery) but the tools he has in return work properly now. In other games they did not.