Well, sort of. But I think you're overstating it. As I recall the way it was explained in Lifting Shadows, it wasn't really that the vocalist was "just the vocalist" and had to just "sing what was written for him." It was more that in this band, the emphasis was on the other musicians. They said basically the same thing to Charlie, as I recall. But clearly, by 6 Degrees, either that expectation had changed someone, or they expected James to be more involved from the getgo and he wasn't getting that message, or they had expected him to be involved, but he had sort of drifted out of the process. Either way, it's easy for us as fans on the outside who weren't there for any of it (or for the years of history between these guys in the years in between I&W and 6 Degrees) to blow it out of proportion. Bottom line is, it seems to have worked itself out just fine for all parties involved. James obviously wasn't offended by it, and used it as a motivation to up his game, which seems to be a win for everybody involved.
the tricky thing is that I&W was written before they had a vocalist. I think they were also keen on keeping those dynamics throughout and who would want to be left sitting around if the band for the most part didn't want him involved? So it seems James spent less and less time with the band, and why wouldn't he? Plus it saves some money if he gets to stay at home in Canada while they write.
I will say this though, ADTOE seems to have made a great formula. I still wish they would just credit the whole band but I don't mind that they actually only credited people that were directly involved. Some songs were only credited to JP and JR and some were the main three but even James got a few credits on songs he didn't write lyrics too.
From what I understand, they all convened, JP brought in ideas like he normally does and some needed fleshed out more. James contributed, flew back home for a while, came back to do vocals and realized it wasn't the setting he wanted, so he flew home and did them on his own terms. JP being the producer and having a strong vision thought that James did a great job but there was a few songs he was very particular about so he flew to Canada to personally oversee a couple.
I really like that they are trying to do what is best for the musicians and the songs rather than just locking themselves in a rehearsal room and coming up with whatever.