I'd argue that Marth over in the west is more known for being "that powerful dude in the Smash games" than for Fire Emblem. Up until the success of the 3DS version, Fire Emblem has been rather obscure outside of Japan.It's hard to say Marth isn't iconic, he's the frontman for the FE series, which has been around as long as stuff like Metroid and Kirby.
The others are a bit more debatable, especially Lucina seeing as she, at best, the third most important character in her game (behind Robin and Chrom).
but my argument is all anecdotal and gut feeling and I could easily be owned by the sales figures of some GBA title or whatever