For some time I have felt that we family researchers should make a concerted effort to change this usage for the sake of consistency and easy understanding. Who cares that "great uncle" and "great aunt" have been used historically if they are simply wrong and add confusion to an already confusing hobby?
It makes sense that the brother of your grandmother or grandfather is your grand uncle. It also makes sense that the sister of your great grandfather is your great grand aunt... ad infinitum back as many generations as you like.
Let's not continue doing things simply because, "That's how it has always been done."
Yours in anarchy,
Nick