I think it's a bit more than that. I enjoy IC's and I hope that they get better in 3.6. The problem is that they are simply bad in comparison to everyone else in the game, I do think they have potential but between most every other character gaining new tricks/capabilities to get around what grab game they still have, the ability of other characters for the most part to separate Nana even though she's much better in terms of surviving than in Melee, makes it hard to play them and do well.
In fact, IC's literally have to work the hardest in PM to keep up with other characters, much less get stocks because their tools with desynchs, etc is awesome, but it takes a ton of work to have those up to par, and a lot of characters that were bad MU's in Melee got better, and IC's lose to quite a few PM characters as well. This + the unreasonable hatred of IC's and the glitches that exist ensures a low number of IC's players. Also, in comparison to everything else I don't think IC"s were compensated enough for the lack of an infinite game.
Either way they are still fun but i'm almost positive they are the hardest character to play at a top level in PM.