Agree with you there. Understanding that, it becomes a tool for personal assessment of one's health, for the n=1. The study results is fun trivia, but not really of much use to compare with one's health.But a lower heart rate actually is good if it's because your training has strengthened your heart muscle, increasing its stroke volume. It's just hard to tell whether your heart rate has slowed down due to a reduction in blood pumped (in other words, lowered metabolism, which is bad) or due to cardio strengthening your heart, meaning it has to do less work to pump the same amount of blood. For most people, it's probably a bit of both.
I wonder if a Peaty runner (assume it's not an oxymoron) having a heart rate rate of 45 would improve his heart rate to 65 and see his performance improve.
How about an ailing grandmother seeing her health improve as her heart goes goes from 90 to 75?
But the body sets its own heart rate depending on what it sees is best for the individual.
My heart rate doesn't really go past 75, and often stays at 65. But I have some issues internally I am resolving, and my body is capping my tissue oxygenation rate, and my metabolism and heart rate is capped as well.
I wonder why the heart rate of a long distance runner is capped in the 40s though.