Well, I think it's a matter of if the essence of the songs is there. I mean, drummers like Peter Wildoer, for example, he's so aggressive that his style of drumming would fill every DT song with balls to the wall bombast. Or at least that's how he sounded on the audition. He's a great drummer, but I could hear at the audition, that in spite of playing the parts correctly, his style just didn't fit DT at all.
With what MM is doing with the fills, I don't think it's any different than what MP used to do when he'd improvise his fills. The essence of the song was still there, and it still felt right, but at the same time, it was just something a little more indulgent and impressive, which is what people generally want out of prog.
Plus at the beginning, I think they were more concerned with making sure the new drummer, whoever it would end up being, wouldn't alienate the fans. So I'm sure that state of mind was always meant to be temporary, just like ADTOE being made for the purpose of proving that they're still the "same band" and will put out the "same kind of music". At this point, I think MM has gotten as much acceptance from the DT fanbase as he we could possibly expect, so there's no pressure to prove that he's a right drummer for Dream Theater, anymore. People either agree that he is, or they want Portnoy back, and I doubt that's gonna change.
Not to mention, like he said, this is from the general fan consensus.