Actually you know what? I will explain why Fire Emblem in Smash is a good thing.
Fire Emblem, unlike other franchises like Mario and Zelda, need new characters to represent the games. Mario has the same cast for most of the games so when you put that cast in there isn't much else you could add. Same thing with Zelda where once you add the main cast there isn't much to add. Fire Emblem on the other hand has a different cast for most of the games so if they come out with a new game, chances are they'll need a new character to represent it since it's cast will be brand new. And yes, while not all the representation is good, (Corrin). It's perfectly fine and reasonable to have a new character each Smash game to represent a new or old game in the series.