My primary weapon against fireblight has been removing susceptible varieties. I have removed around 50 apple varieties which had bad fireblight issues, and all quince and medlar. I don't get much fireblight on pears ever, not sure why.
I don't spray anything for fireblight now; when I had it badly I sprayed everything (copper, antibiotics) any it probably kept things from getting even worse but I was still getting a great many strikes. If you are getting a minority of your varieties with heavy damage you will have much better results removing those as opposed to spraying. Also pruning more open helps.
This spring I topworked King David as it had blighted consistently every year for five years in a row. Outta here! Now I am concerned about Gilpin, it got several blossom strikes this spring. But its a young tree and I will see how it matures.