The movie is suggesting that the criteria for the mission and the fatalistic attitudes of society are somewhat incomplete by showing that Vincent's 99th percentile "grit" has been completely overlooked because of the genetic stuff which is more readily measured.

Perhaps it's true that his genetic predisposition, as measured, is 70th percentile, but there are other relevant factors towards being a good astronaut that aren't so easily measured, to say nothing of environmental factors affecting cardiac health as well as the reliability of the gene-based measurement itself.

> We actually see that he has a heart condition.

Actually we don't. The portions of the movie where Vincent struggles are because he's trying to keep up with the genetically enhanced.

There is a certain probability he will have the heart condition. That actually happened. There is a separate, dependent probability that given he has the heart condition he will die very young. That, at the point of the movie, hasn't yet come to pass. I don't see the problem.