Well you can get away with not adding anything cause you may not have to... Everyone's water is different.This is certainly false, if one is talking about the majority of conditioners. I do not know of any that do not handle both chlorine and chloramine. It will say on the label in any case.
I would suggest that meither you nor any of us can possibly say this unless we are biologists and perform a necropsy on dead fish to find the cause of death. The early stages of a "problem" are usually internal, not external, and the fish may well continue to swim, eat and spawn. This does not mean it is healthy, or as healthy as it reasonably can be.
We know that soft water fish kept in hard water develop blockage of the kidneys relative to the level of calcium, but there is absolutely no external indication until the fish dies. We know that nitrate slowly weakens fish, making them more susceptible to disease issues than they would otherwise be, but there is no external sign of this until it becomes very severe.
The physiology of a fish is unique among animals bcause of their very close connection to their aquatic environment which is greater than that of any terrestrial animal to air. Chemicals in the water do affect them most of the time, seen or not. I know not everyone will agree, and I don't care, but my approach for the past decade-plus has been to add as few additives/substances/chemicals as possible, only what is needed for the welfare of the fish and minimally the plants. I have not the slightest doubt that this is largely the reason I do not have to post asking for help because my fish are doing this or that or dying.
Anyone who has ever tested the habitat waters will not find evidence of these chemicals, and the fish manage perfectly well. I know this is somewhat simplistic, but it has been said and it is true, fish live in clean water, not chemical soups, and you will have success with the former over the latter.
In your situation as you have detailed it in a couple of threads, you do not need the Aqua Essentials. You decide.
To me it's sounding more like an opinion. Not to say you're not correct about some of the things you're saying. Because I do agree, fish don't need these chemicals IN THE WILD and we should be adding as little as possible.
But on the wild they don't have chorines or chloramines to deal with, here they do.
I didn't use Prime because people said that wasn't the safest option, so I went with API instead.
If I didn't use this, the ammonia would hurt the fish. But it hasn't cause its "detoxified".
As far as I know the other tap water conditioners don't deal with chloramines unless the company changed that...
But even if they did it wouldn't detoxify the ammonia... It would just be toxic to the fish then leading to issues...
Plus I think the api aqua essentials uses less per gallon but I could be wrong on that one