I have not seen the YouTube(s) you refer to, so it is impossible to put my comments in perspective. But there is truth in the fact that fish will die from genetic problems that we cannot ever know about unless we are a biologist/microbiologist and can perform a necropsy (the autopsy on animals); and sometimes in such cases it is best to ignore the death. On the reverse side, fish dying more frequently can be due to a contagious disease, water issues, inappropriate stocking, etc, etc.
There is often a desire especially with new and inexperienced aquarists to "do something" if a fish gets "sick" or dies. This is an instinct that needs to be checked. When one understands the complexity of fish physiology, one hopefully realizes how dangerous it is to take some action. The chances of knowing the exact cause of the sickness/death are slim for most hobbyists. With experience we learn to recognize some issues (ich for example) but external signs of a disease are not always identifiable or if they are they may be common to several problems. The inexperienced hobbyist immediately starts adding "X" medication, then when that doesn't work try another, and so on. All of which almost inevitably kills the fish and harms those that may be healthy. If you cannot identify the cause with a fair degree of certainty, it is better to not add medications/chemicals because they will further stress all fish no matter what they are, making them even weaker and more susceptible to whatever the actual problem may be.
More than once I have simply removed a dead fish, or in a few cases euthanized an obviously dying fish, and done nothing more. Water tests at the sign of a possible problem are advisable, just in case there is a spreading issue. And depending upon the signs, a massive partial water change can sometimes be the best and only-needed treatment. All I worry about when I see a dead fish is ensuring there is not something contagious or spreadable.
Recently within the space of two weeks, two of my five Ambastaia sidthimunki died. Both were females (the significantly larger gender). I removed them when I saw them, and did nothing. I have had this group for ten years, and since it has a normal life expectancy of 8-12 years, it is very likely they simply came to the end of their lives. There is nothing abnormal externally with the three remaining males, nor the rasboras in the tank. Fish do die.