It's a magical world

Well, it depends, for sure! The wagashi in particular evolved out of sweets for the tea ceremony, and matcha is actively bitter, so they are basically pure sugar even today. (You probably know all this.) But stuff like cake or whatever is generally much less sweet than the equivalent in the States imo--even in the stereotypical vanilla cake with strawberries, there's just not as much sugar. But yes, from my extremely limited experience of Korean desserts, I would agree that they are less sweet than Japanese ones.