Do you honestly believe, that the FE fanbase actually likes the representation it gets in Smash?
Marth is admirable as a character, but overall he's pretty bland to many and the only nostalgia for him in the West comes from Smash/Melee.
Marth is still popular nowadays, particularly in Japan, where he still receives official art and trading cards. Being popular because of Smash isn't a point against Marth. Not only the interest in him gave FE to the West, his appeal is so big it would be wrong to cut him. Back in 2013 people were worried he would be cut in favor of Lucina (oh the irony) and many celebrated his return. He may be known for "TiPPeR FSmasH!" but so do a lot of other characters like Cap. Falcon, Sheik, Ice Climbers, Falco and Fox.
Roy: For a long time considered the worst FE lord. Also, still Japan only, so no actual nostalgia for him aside from Smash/Melee.
I don't see how being Japan only is a point against Roy when FE6 is really easy to emulate and obtain a ROM, but yeah no defense for Roy. He truly was no one who anyone asked for.
Ike is stupid popular amongst casuals but that's mainly because of Brawl because the performance of his games is what set the franchise downhill to almost being canceled. (No marketing, releasing week of Super Mario Galaxy, etc.) People really appreciate the Tellius games now (see Path of Radiance's value on Ebay) but in the end, Ike was a relevancy character that had missed potential.
The Tellius games are expensive because they were barely printed. Their reception has been going downhill. Many are waking up they are garbage, with sluggish gameplay and terrible design choices. If it weren't for "I fight for my friends" Ike would be horribly unpopular.
Robin: Now this is where the fun begins. Robin seems to have a pretty good rep in the Smash fanbase for being unique and from Awakening, but Robin is heavily contentious in the FE fanbase. He was the start of making overly self-insert avatar characters mainstream, and some see that as ruining some of the most important aspects of the franchise. (Story, characters, etc.)
Yet many were silently on board with Robin because he would be more unique than Chrom, who was supported by autopilot.
Lucina: Another Awakening rep. Up to Smash 4, there were 11 mainline games that weren't remakes, 13 games in total. Blah blah blah...
Costume or clone Lucina got in Smash 4 because she was uber popular between 2013 and 2014 with the FE crowd. The reps are also equally distributed (Marth reps the Kaga era, Ike the dark age, Robin the revival of the series).
Corrin: Overall I bet the FE fanbase wishes Corrin wasn't an FE character. I don't need to go too much into it, but from Fate's story, characters, and how it is overly represented in everything FE after it, people really don't like Fates. Also, as the old saying goes: "Nobody hates FE more than FE fans". People hate Corrin on a surface level in the Smash fanbase but in-depth hate for Corrin goes around in the FE fanbase all the time.
The babies who complain about Corn 24/7 and those who makes memes of them are who give them their popularity. The waifu crowd who idolize Corn and draw fanarts of her also give her popularity. Gotta agree very few asked for Corn.
Don't act like there are a bunch of people dancing around laughing as their somewhat niche little franchise seemingly destroys Smash Bros as a whole (at least that's what I can gather from how people react to it.)
If anything it is the opposite. Many have shown their distaste for Roy's popularity because of "da ph1r3" and debate about Ike all the time. Also contention about memes and jokes being born from Smash, like "I fight for my friends.
.
& 
DUDE SQUIRTLE IS A BEAST!
)
