With the addition of Fire Emblem: Three Houses' Byleth, Super Smash Bros. Ultimate now features eight playable fighters from the Fire Emblem universe. The situation has frustrated fans for a while now, with the most vocal believing that characters from other series deserve recognition in place of more Fire Emblem stars.
It would appear that series director Masahiro Sakurai understands the issue, discussing it in an upcoming issue of Famitsu magazine. An excerpt of his regular column has leaked online, with early translations suggesting that he agrees that there are a lot of fighters from the series, as well as a large number of sword fighters.
According to a translation from BlackKite, Sakurai says that the high number of Fire Emblem and sword-based fighters has simply been decided like that, leaving him to 'proceed as-is'. He explains that new fighters aren't decided by his own favourites - as some fans have theorised in the past - but rather they're chosen by Nintendo.
Of course, it's already been said in the past that Nintendo is responsible for the chosen DLC fighters, but in another early translation provided by PushDustIn, Sakurai reveals that a character he liked 'wasn't given preference'; Nintendo had chosen Byleth and work began while Three Houses was still in development. Byleth's multiple-weapon moveset was included as a way to mix things up.
It's worth reiterating the fact that these translations are from a summary of Sakurai's column, not word-for-word quotes. Should future translations of his exact quotes shed more light on the topic, we'll be sure to let you know.