Incorrect. "Palliative" treatments are likely to significantly increase the chance of survival. We don't know because past victims were almost all treated in locations where truly modern care was unavailable.
Finding out whether treatment can be even partially effective is a plus to this scenario.
For example, prior to the 2001 anthrax attacks we believed those infected died at about the rates for Ebola. We now know that antibiotic treatments, if started in time, are quite effective.
Another example. Until fairly recetly it was believed that rabies was by definition fatal. In the last 10 years or so, several people have survived, due to effective supportive care, not specific treatments, which still don't exist.