If anything, this would strengthen the argument. If the expert was doing an excellent job and making few, if any, mistakes, then the computer must have performed even better, perhaps better than humanly possible. This would strengthen the claim that computers should replace cardiologists in interpreting EKG data.

Irrelevant. The computer isn’t being asked to “practice medicine.” It’s being asked to read EKG data, which seems unlikely to require a subjective element, unlike the practice of medicine in general.

This answer choice suggests that the computer program was biased in favor of interpreting EKG data as signaling a heart attack. It tended to predict a heart attack even when no heart attack occurred. Thus, since we don't know the proportion of actual heart attacks versus non-heart attacks in EKG data, the computer may well be wrong in its diagnoses more often than the expert was. This would weaken the author's claim that computers should replace cardiologists in EKG data interpretation.

We're not interested in cases where EKG data is insufficient to make predictions. The stimulus only talks about cases where EKG data can be used to make predictions. We want to know about whether computers or cardiologists perform better in those specific cases, where EKG data is useful.

If anything, this would strengthen the argument. The premises tell us that this cardiologist was a skilled expert, and still underperformed relative to the computer. So if most cardiologists are far behind this one in their skill level, this makes it seem even more important to replace cardiologists wih computers in interpreting EKG data, as the author suggests.