@crazy4life, that is a preprint that has not yet been reviewed. It may or may not be confirmed for publication and is in disagreement with other publications on the topic some of which have gone through greater review. For example a recent CDC publication found 2+ times less likelihood of reinfection in individuals who had recovered from SARS-CoV-2 then been vaccinated.
Typically in medical research competing publications are published after peer review until an eventual consensus is reached. This normally happens in journals that are not followed by the general public. With CoVID-19 there is great public interest but we need to avoid jumping to conclusions based on early data. Also the media reporting, even medical press, often is sensationalized.
In my personal life I consider a recently recovered person to be as safe as a vaccinated person assuming they have a functional immune system.
Quantitative antibody testing before vaccination would be a useful tool for determining who would benefit from vaccination. Governments and large medical agencies have to be considerate of creating complexity. Most Americans would benefit from vaccination so the easiest route is to require for all. Once the relevant statues are published they may contain exceptions for persons who can prove they have antibodies. A threshold would need to be established for a sufficient antibody level which would require further research.
As far as biology goes I am an amateur but I hope that helps.