Does it matter if other studies have done better? If no study to date has met standards, do we lower the standards until a published study rises to the occasion? I hope not. After all, the point of standards includes defense against confounding---your "other variables", known and unknown---especially in combo with motivated reasoning. During a pandemic, reason doesn't lack for motivation!
As for studies that do meet standards, they are hard, not easy, to dismiss. That work tends to get meta-analyzed and synthesized, not brushed off, at least by the reader community at large. I wish more of it got replicated, too, but that's a different thread.
Meanwhile, we still have to make decisions. But not entirely without scientific guidance. We can reason from studies of how the disease spreads and how potential countermeasures work. We can argue by analogy to what science has revealed about apparently similar phenomenon, like flu. Those aren't scientific arguments so much as other kinds of arguments hopefully informed by science. Pending better science as such, that's what we've got.