Quote from your link:
"We are only now beginning to understand how the complex interaction between
host and algae works and was able to develop over a million years of co-evolution," Guse says. un quote
Unfortunately, we never think of these interactions and instead look for spots. Everyone feels "spots" are the most important criteria in this hobby. Ooh, what kind of spot is this?

When we go to a doctor (I went to 4 this week for a silly Pre-Op) but the doctor never looks at our skin looking for spots. Spots are what we call parasites because we feel that is an appropriate word for an organism that we don't fully understand but we know that we hate them.
Spots, or parasites have been here much longer than us and if parasites were that dangerous, there would be no fish in the ocean because no one dumps copper in the sea to kill them. Fish have no problem living in harmony with parasites just as we have no problem living with ours.
Yes, we all have parasites. Some live in our noses and some in our eyebrows and ears. They don't hurt us but are dancing the macarana all over us.
All fish have parasites and many of them also have worms. Some fish are filled with them as my family was in the sea food business since the Roman Empire right up until the lead pipes killed all of them or turned their minds to mush.
I feel we should not kill the parasites as they are the only thing keeping our fish from being killed by parasites.
Those few parasites we see on the sides of the fish are just there hitching a ride because they can't get through fish scales and a healthy, non medicated fish will have plenty of anti parasitic substances being produced in their slime that they constantly exuding.
The tiny amount of blood parasites suck out of fish gills don't hurt the fish. It's the existence of so many parasites on the gills that limit the amount of oxygen the fish can extract from the water that kills the fish.
It's like if we filled our noses with earthworms. The worms won't kill us but we wouldn't be able to breathe and we would also be walking around going EEww all the time
Healthy fish even have slime in their gills and down their throat which excludes parasites but only if the fish is healthy and living in a natural habitat. A quarantined tank or a tank filled with medication or copper will suppress this process almost forcing the parasites to kill the fish so medication, especially copper is counterproductive.
Also fish are not like most of us. We get stressed if we only have 10% battery life in our Smart phones and we are in a group text with 7 people discussing how horrified we are because our "Clearasil" didn't arrive yet from Amazon
and we are all going to the Barbie movie.
We don't get it that it is not bacteria, parasites or Broklenena that is killing our fish, it's stress.
Stress is caused by captivity but not if the fish is in a place which they feel is the ocean. As soon as they see a PVC elbow from Home Depot they panic. If they "smell" copper, they go nuts as it is a poison and I am sure very irritating.
When they are in a new tank with nice clean and white rocks with no life on them, they get the horrors.
But if the rocks have some natural growth on them and a few "Natural" hiding places which are "tight" and a little dark where the fish can't see us, they are happy. They don't know that we know where they are as long as they can't see us, or our cat. They also don't care if they have to lay on their side to get into these hiding places, they rather prefer it.
I have a couple of Gecko Gobies, I think that have been in my tank for a few years. They are very healthy, I think, because I never see them unless I shoot some worms near where I think they are in the back of my tank and I may see a glimpse of a tail occasionally. Of course I don't want all my fish to hide constantly, but if we want to keep certain types of fish, thats what we have to expect if we want to keep those fish. I had a cusk eel for 18 years and saw the thing maybe 4 times and only at night by using a flash light and that fish was 6" long.
I killed it by accident when I removed a rock and didn't know he was in it. I didn't even realize I had him.
OK, thats long enough for now as it is about 7:00 am and people are going to start to get up so I have to make breakfast.