If Pius XII had come out loud and clear against the Nazis it would look good in the record, but whether it would have done anything to check them or undermine them is pretty uncertain.

What is certain is that it would have triggered off the imprisonment and death of enormous numbers of ordinary Catholics across Europe, together with any Jews or others who were being protected or hidden

Perhaps he should have done it anyway, but I don't think his failure to do this can be written off as cowardice.