“Can we agree that he was an authority on architecture who happened to be a Protestant???”
No, he was a Protestant authority on art and architecture. And although I didn’t say it then, he clearly was an authority of Protestantism as well in regard to Protestant aesthetics or lack thereof.
If that helps you sleep at night. Although, I will expect you to not challenge nor disallow citations from Roman Catholics who expound on their personal opinions of things Catholic and are called "Catholic authorities". Are you comfortable with that?