aw yeah now you're speaking my language. I said a few things about book!grace's response to being ousted from academia in another addition I made to this post, but to expand, I think the subtly altered dialogue in the two versions of his first scene with stratt convey that the two iterations of the character took slightly different things away from the same experience. the in-person "staggering waste of carbon" incident is a movie-only inclusion, and you're right, that's not a very "unsure of himself" thing to do, and whatsmore it's a super mean thing to say (which doesn't seem all that like him) and also simply an innovatively stupid move. like, if he wanted to precisely calculate the best way to explode his career, that would be it. in the book, he says of that paper that he "had enough of the research world and that was sort of a ‘kiss-my-butt’ goodbye," meaning it was knowingly incendiary, but we don't get a similar line in the film.
movie!grace has a few moments were we see him express anger externally: something crosses a line and ticks him off and he screams and hits inanimate objects about it. important to note, I think, that he's never screaming at anyone, the objects he smacks around are mostly his own, and that the one time he does it in front of other people and in someone else's space that he keeps the physical stuff confined to a trash bin and cools down a little before taking to anyone and apologizes afterwards, broadly showing that he's not trying to be aggressive and genuinely does just have a short fuse. combined with the lack of any "I was on my way out of the field and wanted to leave with a bang" lines, it reads to me like he just lost his temper in a really bad way in a public professional setting. he wasn't looking for an opportunity to get out, he had a visible acute breakdown and lost his job. and he remembers that whole episode as "I was fired for standing by what I wrote" instead of something like "I was fired for making a scene at a conference and severing all my professional connections," locating the problem as being that he stood up for himself in the first place.
what I think is particularly interesting is that his conclusion of "I'm a failure, I can't rise to the challenge" looks completely rational from his pov. he cussed out the leading scholar in his field in front of an audience and got fired about it (yeah that'll happen if you do that) and then his big bold idea got roundly disproven (so maybe they were all right to treat him like he didn't matter regardless of how much he believed in the work). "I can't handle the pressure, I'm not skilled enough, I'm wrong about my strongest convictions and I'll suffer pointlessly if I actually try to give it my all" is a reasonable takeaway to have from that sequence of events. he conducted himself poorly and was legitimately wrong, the narrative doesn't validate that he was secretly right to do any of that, it just says that he shouldn't have let it ruin his self-image.
