As for commercially available varieties in supermarkets, I do not perceive much difference than when I was a kid, same goes with backyard grown, in my home town, of Cocoa Beach, out house had a small grove, about 12 orange trees, ( some kind of navel orange ) and 13 grapefruit, 1 tangerine. and although people generally look at the past with rose colored classes, i'd say many fruit I have tried recently are just as good as when I was a kid.
But just like mangoes, you can have the same variety grown in 5 different locations, and get 5 different outcomes. I know the citrus industry is seeing some hard times, with all these new diseases and whacky weather. been reading on how many citrus growers are about to throw in the towel, and change crops.
Today in my yard, the only plant I have consistent problems growing is citrus, every bug makes a bulls-eye for them. scale, fungus, nutritional problems. so I wonder maybe the changes in cultivation is some areas, have changed the quality of citrus. my old trees from my childhood, were never sprayed, didn't even bother fertilizing them, and they were healthy.