Actually, there are a few reasons to want Echo Fighters:
- If you like a character, but don't think they'd warrant a full moveset.
- If the character is never realistically getting in otherwise.
- If you think they could add an interesting nuance to their parent moveset.
For me, Chrom and Ken are the gold standard for Echo Fighters, and is what I think of when suggesting them. Their different properties and new moves provide a twist to their parent moveset beyond "it's Marth, but objectively better", and while I realize most Echo Fighters aren't like this, they quite frankly should be, and if they're not, I don't want them,* so when I say I would like x character as an Echo Fighter, I'm making the assumption that they will be able to have their unique qualities on display even though their basic skeleton is based on another fighter.
*That's not to say I want the other characters to be gotten rid of, just made more distinct.