Is it accurate to say that none of the supplements in our Antiviral Regimen are entirely redundant, that each has some unique and useful properties not fully achievable by the others?

This is quite true and reflects why there are a total of seven in the current roster. It takes that many to provide a wide spectrum of phytochemical solutions for the array of adverse circumstances present in the body, with the huge array of illnesses and maladies of all kinds that have a viral origin often selectively damaging a particular site in the body, whether a tissue that is in a location harboring the virus in sufficient numbers to be a problem or an organ where the virus is largely or totally isolated but preys on that organ and produces a diagnosable malady, given the many kinds of damage and secondary consequences of physiological derangement caused by the viruses directly, and very commonly the adverse effects of immune system attack attempting to rein them in but causing collateral damage. So there is much to do and, given the wide array of circumstances and variables, there needs to be a broad spectrum chemical assortment in the mix to cover all the bases in order to be generally applicable for the laundry list of indications you have researched and summarized.