Tart Honey Crisp
The quality of the Honeycrisp fruits will not be affected by the presence of the nearby Haralson or any other apple tree variety. Unfavorable growing conditions probably account for the lack of sweetness.
Apple fruits exposed to sun are usually sweeter than those that have matured in shade. Pruning to open the tree's canopy is often needed to allow maximum exposure. Thinning immature fruits to reduce the crop load also favors larger more flavorful apples at harvest time.
Leaf diseases may be a factor. Fruit quality often suffers when trees are partially defoliated by leaf diseases such as scab.