But on DT12 they wrote and recorded at the same time.
Yes. That's one out of 3 albums but in that interview he stated he wants to to that more. I'm not sure why people can't understand that?
As Kotowboy said, Mangini was actually relieved to not be included in the writing process for ADToE. He expressed that in several different interviews, so, it's hardly fair to count that album. The circumstances surrounding that album were very unique, and different from the normal routine. He really only has two albums to draw from; the self-titled and The Astonishing. He was included and present for the entire songwriting process on the self-titled, and not included at all in the songwriting for The Astonishing (although, as I said before, he did get to come up with most of the drum parts and arrangements, while sticking to the parameters set by JP).
I get that he wants to be included in the entire songwriting process, and doesn't want to be limited to only contributing drum parts, but he's only had TWO albums to draw from. He's only been in the band for what, almost seven years? It may seem like a lot, but in terms of album/tour cycles, that's nothing! Especially when compared to the amount of time MP was in the band. Out of two albums, he was included in the songwriting on one of them. Just because he wasn't on the following album, doesn't mean that will always be the case. He shouldn't express frustration about how on the first album (ADToE) he wasn't included, because that was part of the terms and conditions - to which he expressly agreed to and said he was "relieved" about. It seems way early in the game for him to complain about this sort of thing.