What I understand is the core structure of glucose and fructose differ enough that the metabolic pathways are different. And also while fructose tastes sweet it isn't under homeostatic control like glucose is. So I think it's important health-wise to distinguish the two.

There are other sugars that either differ only slightly from glucose or are dimer, etc. AKA lactose is a disaccharide sugar composed of galactose and glucose. Compare with sucrose which is disaccharide composed of glucose and fructose.