Punk and Joker are not alike at all, aside from having followers no one cares about...
Though...
Not only that but Punk hasn't come across as psychotic in any way. Orton hasn't either. To be honest I find Punk boring. He talks and talks and doesn't really seem to care about what he's saying. He has a decent vocabulary and an aptitude for using it, but there's not much behind it...But he's charismatic, I suppose : p
Another honest comment, in kayfabe I actually hate the Nexus followers more than I do Punk. Actually, I hate Mason Ryan* more than I do Punk. Otunga and Mcguillicutty come in and get whipped, then Mason Ryan comes in, hits a clothesline or something like it and that's about it for any fighting back. He's annoying because he's a heel, and he comes in and actually foils the face. Charismatic? No. Does he serve his purpose/role? Yes.
My apathy towards Punk is probably due to the booking more than anything. He has the potential to reap the benefits of his followers getting the advantage, but he gets headbutted or hides under the ring, or does something else cowardly and it just makes him look weaker than his group. Stupid, stupid.