People don't coplain that there's more mario characters than fire emblem characters because mario is nintendo's flagship franchise, so I'm pretty sure people would expect a lot of mario characters in smash because of that. But people don't really know fire emblem as much as mario so that leads it to being a more obscure franchise. And usually the fire emblem character is someone no one asked for. The only mario character that people didn't want too much is pirahna plant, but now it seems like sakurai is just putting every fire emblem character no one wants in smash bros.
But I can understand your point. Even I used to think that people should be complaining about the mario characters instead of the fire emblem ones.