"But "reverend" is a Prot term."
For some reason, I thought "Rt. Rev." (Right Reverend) was a proper formal address for a priest.
I think if you're addressing a letter to a priest, you use "Reverend," and "Right Reverend" for a monsignor. I've never heard either used in speaking to or about a priest. (Doesn't mean it's not another new-fangled innovation; I also recall when the priest who said a Mass was the celebrant, not the presider.)
It may be a regional thing.
In Milwaukee, we were taught(!!!) to avoid the use of the term "reverend" when speaking of priests, who were to be called "Father."
The idea was to distinguish between the Prot 'reverends' and the Catholic 'Fathers.'