I wouldn't exactly compare it to an amputation, for certain patients it may help with tissue oxygenation at a pretty basic level. You wouldn't write off giving Covid patients supplemental oxygen because it doesn't directly work on the virus itself would you? How about BiPap? Prone ventilation?
It isn't new science, but a new method/application of an established treatment. When I worked on NICU/PICU transport team in the late 90s, nitric oxide was in established use then for premies with severely compromised respiratory systems. Viagra is just a different way of getting the same effect.
For those not familiar, Viagra and its cousin medications help improve blood flow by relaxing the walls of certain blood vessels. That can help you get an erection (if your issue is a blood flow problem) or in this case, it is thought to be improving blood flow to and from the lungs by relaxing blood vessels in the pulmonary circuit. Getting what functional lung tissue remains to work a bit better.
Though I do agree that nothing has been presented to make any case for it helping prevent it, or do anything outside possibly helping people who are already severely compromised by the disease and at a high likelihood of death.