That's actually a really insightful analysis and I agree with everything you've said. So how would you fix this if you were in charge?
For Fire Emblem specifically, it's kind of hard. The problem is ingame, Marth, Ike, Roy, and Chrom are fairly serious, and Ike's uniqueness comes from how he isn't a lord so he's not as polite as others.
Personaly, Ike is fine. I accepted him in Brawl quite warmly. He played very differently from Marth and it translated well into his gruff and muscular appearance, especially in his Radiant Dawn costume.
Roy? Well Roy wasn't very unique in personality in his own game. They made him a better clone throughout the ages, though, but that's really all he has. Otherwise, replacing him with Ike in Brawl was really the better choice. If we had to cut FE clones, Roy probably would be the one I would not cut because he's the slower alternative to Marth without being Ike. If Wolf is fine to people, then so can Roy be. If people wanted Roy back to a point he was Smash 4 DLC, keeping Roy is a good idea.
Lucina and Chrom? Cut. We already have Awakening representation. It would allow people to see the more unique attributes of Roy and Marth too, if any. Lucina was already controversial upon reveal, and Chrom isn't making it better. People have been shown to be open to FE rep if they play differently, and not by just giving Chrom Ike's up-b. As a result, it would also make people more open to other FE characters by just decreasing how many Marths there are. New characters would as a result be given greater impact instead of just being "another Fire Emblem character."
Robin is perfect. I wouldn't change anything about him conceptually. One thing that makes lords feel the same is that since they have their legendary plot sword, they never tap into how weapons actually wear in FE, which is really big. Robin takes full advantage of that and he brings magic. Two things that represent Fire Emblem extroardinarily and here they are in one character. Conceptually, it's why I'm happy Chrom wasn't in Smash 4 when we have a magic man instead.
Corrin I wouldn't cut. They did their hardest to translate how he is in game into Smash. With that said, I would add to his representation. Give us a Fire Emblem Fates stage and more remixes than just Lost In Thoughts All Alone. Maybe even have Xander or Ryoma be an assist trophy. Aesthetically, Fates is more interesting than what Corrin makes it appear to be and he could be given a greater identity because of better representation.
Speaking of stages, I want better stages. Castle Siege doesn't take from a specific game scenario and the coliseum is very lifeless for something that's usually the riskiest, money-making, game-breaking mechanic in FE. Arena Ferox is a good start but platforms never really sprung up from the ground and I don't really remember it much from Awakening. I think if they took from specific chapters more, it would better represent what goes on, especially if they take full advantage of backgrounds. Maybe in Fire Emblem 9, where you're on that bridge with pitfalls and ballista, you could make that a stage and carry it over to Smash as stage hazards while dragons harmlessly fly around in the background. Or in Fire Emblem Fates, maybe you could have the Hoshido town hub and it switches between looking active, beautiful, and Japanese to ransacked by that one early game dark sword. Imagine Battle Before Dawn, FE 7 Chapter 26, being translated into Smash where Ursula in the background summons lightning. Maybe have an FE 1 or 3 map where a manakete stage boss comes in. There are so many chapter set pieces to where I think that is where inspiration should be drawn from.
In terms of newcomers, you already saw my thoughts on that. Lyn and Hector could very well work and are warmly requested to this day. Especially Lyn due to popularity.
For future reference you'll get in trouble with the mods if you double post, edit the second comment into your first post in the future.
Noted.