>>23049218Helioptile and Scraggy are modified lizards. Scraggy is based off of a thug, which reflects in its evolution; Charmander and its evolution Charizard is a straight-up dragon.
Clauncher has jointed appendages, you can't see it well on the official art. Look at the model instead. The claws are "simpler" because it's a shrimp as opposed to a crab.
Goldeen is a goldfish, where Finneon is a butterfly fish. Different types of fish have different patterns.
Raticate is gruff to highlight that it's a "dirty" animal; comparing it to Minccino is poor choice. The simplicity of the hair is because Minccino is a fluffy chinchilla. This reflects in its evolution where it gains a fluffy scarf.
tldr apples to oranges, they're different animals with different design elements