I used to work at an old estate where apple trees were an ornamental fixture lining the very long driveway. If an apple tree died it was replaced with whatever variety the caretaker happened to find at the local nursery.
Amongst the older trees were a few old strain Yellow Delicious and some of the replacement trees were newer strains. The old trees produced richly flavored apples of highest quality and actually did so most years without any spray.
When I put the trees on a spray program the newer varieties of Yellow Delicious started producing smooth skinned fruit that was prettier to the eyes than those old strain apples, but the beauty was entirely lost on the palate. They were bland imitations of the Yellow Delicious variety that originally won apple celebrity. They also ripened over a week sooner.
Apples evolve and devolve as growers and breeders seek different qualities and new sports are selected. The demise of Red Delicious through this process is well documented but I’m sure it has happened to many apples. I actually prefer some of the new strains of Jonagold to the original, so it can probably go either way, but too much attention is paid to cosmetics.
I don’t write this to dismiss the importance of local conditions on the quality of any given variety- I think that is much more often a crucial issue, but I am glad of having the opportunity to taste Yellow Delicious in the form that earned it the name.
What the original Yellow Delicious is, IMO, is a smooth skinned russet apple, which tend to be richly sweet. In the effort to improve it they removed a little too much of that russet quality.
I still manage a few of the older strain trees at sites and am always surprised at how good they can be and how easy they are to grow.