This is a discussion with nearly unanimous agreement that poor ATC working conditions are causing Americans to die in preventable aviation accidents.

Maybe this is the one evidence-driven case where you can be open minded about the value of a public employee union?

Nope. Public employee unions bring zero value and this incident is not evidence to support such unions. Relying on unions to act as ersatz safety regulators would be stupid, just completely the wrong approach. Decisions about things like ATC procedures, staffing levels, and training standards should be the responsibility of apolitical career bureaucrats.