I don't necessarily disagree with you, but you are way too hasty to come to your conclusion. We would have to take the lower number of 75% if we are seriously going to screen the population to be safe. The prevalence of HCM is about 2/1000 (1) in general young populations. You'll miss 1 case out of every 2000 people screened.
This would be acceptable, as you'd catch 3 that wouldn't have otherwise been caught (keep in mind the episode of presentation doesn't have to be death, it could be syncope, angina, SOB, etc), but there are going to be a ton of false positives due to the natural septal enlargement of athlete hearts (2) due to athletic conditioning, and they will have to undergo EHCO afterwards. Add to this the multitude of other incidental findings the EKG will pick up and you have on your hands a real debate about the effectiveness of using EKGs to screen for HCM in athletes. In short, when considering the PPV in the context of the low prevalence and highly confounding nature of athletes, the EKG is a very debatable screening tool.
Just saying, you seem very sure and it doesn't appear you've fully thought this through from an epidemiological standpoint. I would bet if you did a long term screening study of EKGs in athletes you would find no real decrease in mortality and a huge increase in medical cost. But, this study is definitely warranted as the question has merit. On a separate note, do we know for sure it was HCM? Could have been a lot of things.
1.
https://circ.ahajournals.org/content/92/4/785.full
2.
http://www.ncbi.nlm.nih.gov/pubmed/2960727