You're defining hard in a strange way.
It's harder in the sense that it requires more actions to yield the same amount. There are more measurements to be made, more environmental factors to control, more, more, more.
It's a complexity issue. In soil, you can essentially put the stuff in dirt and water it and you'll get some bud (even if its not the best). There is no such analog to that experience in hydro cultivation.
It's much easier to burn plants in hydro, you literally introduce several families of pest species (slime/ types of mold/types of bacteria) which do not thrive in soil environments. Just by complexity alone its harder--now realize that nutrient scheduling and feeding is waaaay more nuanced in hydro than elsewhere. It's a recipe for increased difficulty from soil, it just IS that way.
It's not a value judgment on either style--its more a caution for new growers. If we had to rank these things in ease of use I think RDWC and UC are somewhere on the far end near difficult--and soil is essentially the starting point.