Some aspects of jigglypuff's technical game are critically hindered, such as methods used to get rest in, spacing (kind of), DI/SDI, punishing things that only take a bit of skill offline, and others mentioned earlier in this topic.
However, some moves gain some to much importance. Dair is one. It's harder to get out and respond afterwards, even when shielding, so jigglypuff has some liberties to follow up with another attack, grab, or even another dair.
Pound is easier to hit with, because they have many less frames to respond, and by the time they see it come out, even if they have quick reflexes, it's hard to position themselves for the defense.
Rollout's better, but it's still pretty bad to more skillfull players. I use it just for kicks and giggles if I actually predict right and hit someone in the air from it (usually guess when they're going to jump and time it then, or the tippy top of their shields)
Working around shields is a lot different on wifi, because it'll be very hard to time your bairs. That's why I think dair is more important against lots of characters online than bair spacing is, even though bair spacing isn't nerfed too bad online.