No, I can't prove that stress weakened the immune system and made the fish more susceptible to disease. But, you can't prove that it did. You have not provided any evidence to the claim that 60% of fatalities in fish occur because of stress. So, while I respect you and your opinion, I also must disagree.
I also respectfully disagree with the notion that you cannot have a disease-free fish. Displays like the Aquarium's Black Tip Reef have over a thousand individual animals. This would not be possible if any single one of them had a communicable fish disease. Sure, sometimes individual fish may get infections and need to be treated, but diseases like ich, velvet or Brooklynella would devastate that display. We don't have the resources to quarantine and medicate every animal in that display. So, we QT with an almost militant discipline, and interestingly, no diseases get in the tank.
You don't need to do a necropsy or to gather data to make informed descisions. You have the experience of reefers like
@Humblefish,
@4FordFamily and many other experience fish disease veterans who have already done the research for you. Fish don't die without reason. Does stress likely play a part in fishes getting sick? Sure. Have you, or has anyone else, successfully quantified that? Not that I am aware of, although if you have these resources, I'd love to see them. Quarantine tanks, if properly set up, are not that different than display tanks. A display tank has a way to remediate ammonia and plenty of hiding places. So does a good QT. There are some fish that are ill, sick, or injured, and are just going to die in QT. Putting them in QT didn't make them die though. You advise me to look outside my own experiences and question my hyposthesis, but again, with respect, your experience is just an anecdote too. I'd advise you attempt to broaden your horizons as well. Talk to people who disagree with you, not just those with whom you agree.
We don't just necropsy fish, we necropsy every single animal that dies. Every snake, every frog, every turtle, every eel, every ray, every skate and every abalone. And as I said though, I cannot release that information publicly. We partner with Johns Hopkins for the necropsy services and there are confidentiality agreements to which we must adhere. Fun fact, I'm also not allowed to share any pictures taken in backup or non-public areas without express written permission of my supervisor. I value my work at the Aquarium much more than I would value losing it to share confidential necropsy reports with you, especially since it does not sound like any information will convince you that QT doesn't kill.
This is unnecessary.
All you need is a standard 20g - 30g aquarium, a heater, a pump, some PVC elbows and an ammonia badge.