I see, thanks.
I’m not sure how rare viruses are, but many viruses are listed to be spread by grafting (which obviously wouldn’t happen naturally). In a more natural setting, I would think trees are used to defending against viral vectors and trees with poor defenses get culled by mother mature. But nothing about growing cultivars of same clonal trees is really natural, so in the end fruit trees have much greater vulnerability to viruses and other disease.
Being in humid area, I would rather have fire blight resistance. If the tree is vulnerable to virus and I did introduce a virus to the tree, I’d rather have the viral tree die before spreading the virus to others.
Some other resources also: