Yeah, I don't think JP is passive at all. Not commenting on something =/= passive. Mike P's behavior seems to be slightly more on the passive/aggressive side, with all the strange facebook "likes" and hit-and-run side-comments and whatnot.
To answer the question, I don't think DT would have produced an album as good as ADTOE with Mike P. In fact, Mike's been pretty clear that he's not a fan the record. I think it would have had that slightly more "rushed" feel that the last four Dream Theater records have had, and it would have certainly included Mike Portnoy's harsher vocals and more of his thrash metal influences. Since I'm not a fan of any of those things, I think there's no way I'd have liked the album they would have written with Mike P in as much.
Then again, if DT had indeed taken a hiatus, it would have given the members even more time to focus on writing, and we might have wound up with a double-album or concept album that instantly would have become a DT "classic", which I'm still not sure if ADTOE is. Right now, I'd rank it at 5th, with a pretty decent jump in quality to it from what I consider DT's "perfect" albums: SDOIT, SFAM, Awake, and IaW.
So I tend to agree with Kev. It would have been good, just not great.