Well what's interesting to you doesn't necessitate what's interesting to everybody. I know some people who love the first party reveals and are ambivalent to the third party characters. I wouldn't want the game to revolve around their tastes, just like I don't want it revolving around yours, or even mine.
Eeeehh people like to say that Fire Emblem gets special treatment, and I won't deny that it gets a lot of love, more than other franchises who arguably might need it more. But at the end of the day the series' representation in Smash is mostly the benefactor of circumstance.
By sheer coincidence there just so happened to be a mainline Fire Emblem game launching around the time of each Smash, and each one introduces a new playable character with their own wacky cast of characters. As established by the Pocket Monsters of yore, a series with a revolving cast get a new character in every new Smash.
And Lucina just so happened to be close enough to Marth that they could make a clone out of her. And Corrin's game just so happened to release around the time of the Smash 4 dlc...at least in Japan. Admittedly Corrin's inclusion was a stretch that even Sakurai was iffy about, and I think we all could've avoided a lot of turmoil if they just didn't go ahead with it. But whatever, past is in the past.
And by nature of Everyone is Here, all the FE character's we've amassed are now all back with no opportunity to trim the fat. Chrom was a big fan request back in the day, so they make him an echo too. And then Three Houses just so happens to release while the first Fighters Pass is being planned, leading to the blank-faced teacher. And now we have a million blue haired swordsmen.
It's a lot of lucky happenstances that to FE's prominence, it was never the intention from the start. The team even seems a bit self-conscious about it, which is both funny and sad because you know that means they see all the hate these guys get. I definitely think their numbers will drop by a few next game.
Thank you for coming to my TED Talk