Well let's think about it. It's true that Fire Emblem has a lot of clone characters compared to other series, but Roy was a relic of Melee and Lucina was supposed to be an alt costume for Marth in Smash 4 and Chrom was an echo fighter because he was considered for Smash 4 but didn't happen for reasons. But other than those three everyone else has something to set themselves apart, Marth was the first character FE character, Ike is the slow damage dealer like Ganondorf (who copied some of Ike's moves), Robin is the zoner that can handle himself if the opponent gets close (he also doesn't have a counter making him more unique than the others), Corrin has his side-b crap, his neutral-b, and his sword hitting while charging smash attacks, and his counter hitting both sides of him. Byleth is the only one apart from Robin who does a good job of representing the side of Fire Emblem that isn't just swords with his attacks using his spear, axe, bow, and whip sword. Now with basic counting we can see that 4 of the 8 are truly similar but Roy's rush playstyle differentiates himself from Marth's precise spacing playstyle and is completely different Chrom and Lucina's "Me swing sword" playstyle. 2 of the 4 non Marth clones each have different playstyles with Ike's slow but strong strikes, Robins magic and weapon durability making you think when the best time to use them would be, Corrin, and Byleth's slow but precise strikes. So in conclusion, if we do what the game does and not count echos as their own fighters then only 2 of the FE characters are copies which even then, Roy's playstyle makes him more than just a clone, and post-Melee fighters have unique differences from Marth. And now onto Corrin, in Smash 4 people didn't complain like they do now about Fire Emblem, some franchises got more newcomers than Fire Emblem and all the new characters like PAC-MAN and Mega Man drew everyone's attention and Robin being a completely unique fighter is what everyone sort of focused on when it came to movesets. If I'm not mistaken, Roy and Ryu were announced at the same time and unlike nowadays, Roy was a popular request for a returning fighter and if people didn't like that, they had Ryu who is the mascot of the biggest fighting game franchise in the world making him a more than worthy addition to the cast. Corrin however was not a popular request since his game hadn't even come out worldwide yet and he was getting the second-to-last spot of the Smash 4 DLC.