I don't get why people think Fire Emblem is any less deserving than Pokemon and Mario to have 6 reps. It's been incredibly popular as of late and they certainly have enough characters to work with.
Because they didn't get a [insert another serie here] character of course!
As a Zelda fan, it's been some years that I've been waiting for a newcomer. It's one of the most iconic Nintendo franchise, ect... But it's ok. Compared to many people, I see all the content Zelda got besides the playable characters: assist trophies, items and stages, the serie is still well represented. Plus, Link Zelda and Ganondorf are technically all that we need.
But enough about Zelda. Americans and europeans are still not really that much familiar with Fire Emblem, yet it's a BIG thing in Japan.
I'm not shocked by the Marth / Ike / Daraen / Corrin roster. (also, it's good that Robin is Daraen in Europe, because Robin / Corrin sound too close
). It's diversified, the characters have different abilities (brute force, magic tomes, dragon transformation...).
Lucina is a pure bonus, and Roy is definitely more a Melee fanservice more than "another swordman".
And the serie have only one assist and no items.
The serie does have a lot of characters, but they are all main characters, with their distinct gimmick.