Hell I wish he had stuck to that in the first place. One can hardly begrudge a physician his choice of medical specialization, and I certainly can't comment on his qualifications there, although he is currently board-certified only in diagnostic radiology, no longer (since 2017) in neuroradiology.
Be that how it is, since Scott Atlas is not certified in a field closer to the post to which had Trump appointed him --e.g., immunology, virology, public health administration-- then Trump's questionable pick will forever remain linked to nothing more than Atlas' reputation for conservative views on health policy in general (via past work for Giuliani and Romney campaigns and a position at the Hoover Institution).
But the most relevant fact regarding the temporary appointment as Trump's "coronavirus advisor" was simply that The Don saw Scott Atlas on Fox pretty often last summer, and seized on a potential loyalist.. a guy who was good for no more than a boost to Trump's ratings from die-hard supporters, in the run-up to the 2020 elections.
That was how much Trump cared for public health... picking an advisor primarily because Fox News fans really went for a medico who ran with libertarian resistance to masking and social distancing mandates. This in the face of a global pandemic, when the most effective measures short of a vaccine were and still are those two measures.