He is difficult to master.
Ness has an excellent recovery if you can master him (Huge second jump, lots of distance covered by PK Thunder 2), but if you do not master him, he will fall to his doom. This will inform you a lot about how excellent Ness can be. According to NAKAT, a professional tournament player, he is in the top five of characters.
Also, Lucas is very different from Ness. His only similarity are PK Fire, PK Thunder and PSI Magnet, along with some physicals like his forward smash. But even their PK Fire and PK Thunder are quite different (Although I personally think Ness has the better specials). But if Ness has been buffed, Lucas probably has been, too. Ness' specials are also the same, but they have got plenty of buffs, like how PK Thunder's "tail" damages now, how PK Fire goes farther, etc. How the differences have been set up between the two, I still think Ness would be better than Lucas, but Lucas definitely has the potential to be a great character, too. In the MOTHER series, Lucas is hugely underpowered compared to people like Ninten, Ana, Ness and Poo. Hopefully, this will change in SSB4.