I would expect apples that get exposed to full sun would have more sugar and taste better than ones hiding under all the leaves. That would apply to other fruit trees as well.

Do you mean will all apples on the same tree taste similar, regardless of how and with what they are pollinated?? Yes, with the conditions listed above :-)

As stated already pollination of each apple can be different but that won't affect the flavor or sweetness. Sun expose and other factors can and do affect fruit quality. In my experience some stone fruits are affected more than apples. Apricots are usually several points higher brix for upper sun exposed fruit than for those lower in the canopy. The upper fruits also mature sooner. Nectarines and pluots can vary by huge amounts fruit to fruit. Brix can be double in some fruits compared to others. More usually brix might vary by 5 points, maybe 10, rarely 15. So having 15 and 25 brix fruit on the same tree is certainly possible. Again I think pollination is not the controlling factor.

They will vary, maybe not detectable by eating. Sun, water fertilizer, pruning and others all factor into flavor.

The weather...lots of rain = low in sugar and taste especially close to harvest time. More sun = sweeter.

When I pick fruit from my Granny Smith apple tree in Oct/Nov, the skin is green and the flavor is acidic/tart with relatively low sugar. If I allow some fruit to remain on the tree until Jan, the skin turns to yellowish/green and becomes much sweeter and less tart.

As fruit is growing, leaves produce sugar and this sugar is "translocated" to the developing fruit, where it is polymerized into starch (long strands of sugars). As the fruit matures, the stored starch is broken down into the sugars which we can taste. I presume that in the case of Granny Smith apples harvested at the traditional time (when the skin is still green), that much of the non-structural carbohydrates are still in the form of starch; allowing them to remain on the tree longer results in the conversion of more of the starch into sugar.

It could vary a lot. We picked apples this year in orchard. Apples from the same tree varied from completely bland to really intense taste. I found that apples with russet marks(even for kinds that normally do not have them) have better taste.