I do not know my soil pH, but I know the soil in much of my yard is pretty terrible. I am on top of a limestone cliff, above a creek, which means that all the nutrients that would have been in my soil have leached away or been washed into that creek over the decades. And before I moved in, my yard had sixty years of being mostly grass with some wooded areas (which have good soil) on the periphery.
But, I believe you have identified why your yard is filled with disease. The pests and diseases have nowhere else to go if you are surrounded by privet and hackberry. Hackberry is a native tree but one that is quite disease and pest resistant. Privet is a non-native invasive because no diseases or pests attack it; it is outside of its native ecological niche and nothing in the United States has evolved to keep it in check (except me and other people who attack it vigorously whenever possible). Your yard full of garden plants must be very inviting to every insect, disease, and fungus that happens to wander through. Poor air circulation during our hot, humid summers just adds another issue. I am lucky in that my yard has no privet but unlucky because I have wisteria and English ivy.
If you do not mind me asking, which historic Middle Tennessee downtown do you live in? I am an architectural historian and historic preservationist, and Middle Tennessee has some great historic architecture and landscapes which are being rapidly lost due to demolition and urban sprawl, something I am not a fan of.