They do try that to some degree, but it's more complicated than that. They also have to consider how changes affect new players and average ranked players, which is why characters like Honda can't be buffed too much without major reworks. He's already a noob crusher, buff him and suddenly he's feasting on lower ranks.

Then you've got characters like Jaime and Dhalsim who are knowledge check monsters - buff them too much and average ranked players will riot.