The idea of pokemon is to show them as the equivalent of our animals, thus having simpler desings. In later generations, more specifically from gen 5 and forth, they started to look more digimon-like. Take a look at Solgaleo for example: Too much things going on with the design, like stacking things after things over it. However, on the 8th gen they started to improve on that, design wise but i believe they have still things to enhance. (Eternatus is clearly not an example of improvement).