My stance on FE characters is that I am fine with their inclusion as long as they are unique and fun enough to play as. Heck, I'd be fine if they kept the FE roster the way it currently is.
However, as somebody who doesn't have much attachment to the series, I wouldn't mind in seeing some of them go. I wouldn't choose to cut them, as they are enjoyable to play as, but if I was forced to make a choice, then I'd get rid of one.
Marth, Ike, and Robin are fine in my book and as somebody who grew up playing Melee, I'd even have Roy stay, too. I would say cut Lucina, but that would be kind of weird since clones don't take a lot of time to add in.
I used to hate Corrin, but I've grown to enjoy his/her moveset. However, I would honestly cut Corrin if I was forced to decide.
Needless to say, we say that Sakurai added too many FE characters, but it's a lot harder to decide which one since each of them stand out. It's probably why I don't mind the amount of FE characters as much as others. They may be from the same series, but each of them are unique and as much as each of them use swords, I believe Sakurai made some great calls with this selection.