If there is a visitor with every patient then patients are much more likely to receive proper care, that is NOT supposed to be to the exclusion of other patients, it’s just a mechanism of having someone to advocate and call attention to things they may miss and hold workers more responsible than if nobody saw what they were doing. Similar to the role of a mashgiach in a restaurant.
I understand it can also have a negative overall effect but you haven’t proven that the risks outweigh the rewards, you’ve just ignored the rewards of the system that is ALWAYS in place, for good reason.
1- A mashgiach is suppose to know the halachos of kashrus with which he checks the employees, while a layman visitor does not actually know healthcare with which to check healthcare employees. A common example of this is when IV pumps start beeping. Nurses tend to have a general feel for when to check on a patient, while a visitor often freaks out when it starts beeping, and goes and distracts a nurse while they are doing something else for another patient - potentially leading to a preventable adverse event.
2- It is not universally accepted as you posit, that visitors improve outcomes for patients. A simple Pubmed search on this topic would show you how many different research pubs have been written on this topic that dont have as much certainty as Shevy from Lakewood
3- Even if you were to argue that every patient's care would improve with a visitor, it is obviously not possible for every patient to have a visitor (some are widows, some have kids out of state, etc). Is it ethical in a triage situation that those who are able to have visitors be granted better care than those that are unable? Thats just as bad an allocation as saying that those who are currently on ventilators get to keep it more than someone that needs it tomorrow
4- Until you do a randomized control trial, where some hospitals are granting visitors and some arent, you will never be able to *prove* anything. However, it is compelling that at this moment that visitors are just massive fomites and a very big public health concern in hospitals, and should be banned. And the infectious control managers at 10 of the top hospitals of the country have clearly arrived at this realization.