Please. I'm not one to defend Portnoy, but if you don't think this is people having something against him I don't know what to tell you.
But outside of DT, with musicians like Michael Akerfeldt and Steven Wilson (better musicians who offer far more range in their work) - he's just not needed as a creative influence.
I'm not sure I get this. How are Steve Wilson or Michael Akerfeldt better musicians than the guys in Dream Theater? Petrucci can play guitar better than Wilson or Akerfeldt. LaBrie can sing better than Wilson or Akerfeldt. Jordan can play keys better than either of those guys. And creativity is subjective. And what is this range you're talking about? I don't see how either Opeth or Porcupine Tree are any more diverse in their respective styles than DT. I'd actually say Opeth is the least diverse in terms of range when compared with DT and PT.
While I can understand why people might thing Mike isn't the best fit, I can't understand how people could think Steven Wilson or Michael Akerfeldt are are somehow "better musicians." Then again, I've never understood what's so great about the "songwriting" of PT or Opeth. I like both of those bands, but not at all for what people call the "songwriting." In my opinion, both those bands are about on the level of DT from a songwriting perspective, aka they're pretty average.
And Steve Wilson can be an absolutely fucking terrible lyricists in his worst moment, to the point where I'd rather listen to Systematic Chaos. There, I said it. But I think it boils down to people, quite ironically, having a very specific idea about how they want this project to sound. People want this project to be dark, slow, moody, electronic, atmospheric, with prog tendencies to a minimum, etc. I mean, as I'm reading this thread, I'm already getting the impression that people want a mix between Blood and Damnation, with Steve Wilson on vocals. They want it to be a style that Mike Portnoy hasn't been heard playing too much of, so of course people are going to say they'd rather hear someone who's already done that, like GH, on drums. They don't want to hear Portnoy have a creative influence, which, though a shame, is understandable, especially since (as many here have already pointed out) Portnoy seems to be the only one suggesting he was ever going to be a part of this.