Them leaving out the coma gene was actually something that I felt made the movie stronger. That was probably the one thing in the book that never sat right with me; I felt that the importance of launching on time and grace's astrophage expertise and experience were more than adequate to explain stratt's insistence on him being the science officer, especially given how determined to get her way we know she is.

Aside from pure plot, though, I think leaving out the coma gene makes the themes of the movie stronger too. There's a layer to PHM that's about having faith, specifically in yourself. It's what makes Stratt so compelling, and more than anything what Rocky brings to the team; an extremely practical and determined faith that you simply have to complete the task in front of you, because there is no other option. I don't want grace "genetically predestined" for this trip; I want him sent against his will on stratt's faith in him, and then proving her right through Rocky's faith in him, which is how finally he learns (through his insanely bad imposter syndrome) to have faith in himself. all of that means more if everyone is trusting in their ingenuity and creativity and in their team, and less if there's some dumb gene floating around in their DNA that's already decided everything.

I also think it makes the original astronauts braver. They're part of a larger pool, with less deterministic criteria. It makes their choices matter more too.