I don't really think this letter is trying to be anything other than an articulation of a value judgment made by people with a certain perspective that gives visibility not just into the effects of COVID-19, but other public health issues that disproportionately affect black people.
I'm also not super convinced that "the public health sector" was never receptive to questions about economic tradeoffs. We have a dysfunctional federal government and the same in many local jurisdictions, but where I live the local public health institutions have been working hand in glove with state and local governments to open as quickly as possible while staying abreast of the disease's spread.
The problem the public health sector has worked itself into is that it dismissed any attempts to analyze “trade offs” when we were talking about economic trade offs. So now they have to pretend like we’re not talking about trade offs at all. Hence the completely non-sensical premise that protests are okay because police brutality is a public health problem.