Why exactly do people say Ness is broken?

I'm a Ness and ROB main, but curious why people are so against Ness? His moves are good, but I personally find them to generally be easy enough to punish (especially when he hits himself with pk thunder and misses, and anything to deflect projectiles) and of course easy to use. I see how spamming side B can be annoying, but you can usually walk away from it.