As I said earlier, popularity doesn't factor into it as much as history. Sakurai gave us some background on FE in the video presentation and as I also said earlier, Smash and FE have been closely linked since melee. There's no such thing as fighters that "need" to be in there when it comes to Smash. Smash is Smash.
I also don't care about clones. I like being able to pick between characters, for example; I don't like using Marth, but Lucina is one of my mains. Clone arguments usually get a snore from me. I don't fuss over them because I'll just use who I like; which by the way is what Smash is about.
By that logic “Pitfall” should have more representation than Super Mario. Pitfall was an Atari game so it has much more history. Popularity is by far the more important factor, and having 8 characters from an incredibly niche series is not a good thing. If you don’t care that there’s close to no difference between Marth and Lucina why do you need them as separate characters? Why not just have them as separate costumes like Bowser Jr? Saying the argument bores you because it doesn’t apply to you doesn’t invalidate the argument. The fact of the matter is that the vast majority of people already disliked the ridiculous amount of FE characters in the game, so adding another isn’t good.