I agree that you can do TTM and hyposalinity without a vet. However, if your goal is to eradicate 99% of the things that can wipe your tank, those two methods alone won't do it. Neither method will get rid of most internal parasites, some flukes, Brooklynella or Uronema. These require medications that are already unavailable to most non-US hobbyists and they absolutely have the ability to wipe a tank. And, as
@ngoodermuth pointed out earlier, many fish can't be saved once they show symptoms that a vet can identify to write a prescription for. Not everyone is lucky enough to have a vet willing to do that. Most people I know have been unable to get a script for CP without bringing a sick fish in.
I won't encourage anyone to break laws in pursuit of this hobby.
So again, this is what is motivating me... how do we help the member in Canada that has a fish with signs of Uronema in their tank? What QT advice to we give them when they can't use copper, anti-biotics, anti-fungals, or de-wormers? Too often I feel it looks like we stop trying to help them when they can't access the med's we typically use. How much longer before we can't get those meds and what will we do then?