The issue with Corrin and Roy was never that they weren't "unique" enough. It was that there are several other characters that could also be unique, but were passed over in favor of a non-character.
No one (at least no one sensible) has any doubt that any Fire Emblem and/or "sword wielder" could be unique. And if they do, I can point them over to Soul Calibur where 90% of the cast uses a bladed weapon in unique ways. At the same time, Smash is more than function fighter and people have likes and dislikes for actual character, which is why MvCI and Soul Calibur 5 got panned for gutting their rosters for functionally similar characters.
I feel like Roy's at least fine in this regard now.
Thirteen?
...am I missing something? Did they just secretly add whole Heroes roster to Smash?
8 Pokemon characters and 5 FE characters aside from Marth and Chrom.
The initial post said that
both Pokemon and FE characters always added the newest member:
Pikachu and Jiggs coincide with the releases of PKMN RBGY
Mewtwo coincides with PKMN The 1st Movie
Pichu coincides with GSC
Roy coincides with Binding Blade
PKMN Trainer coincides with FRLG
Lucario coincides with DPPt
Ike coincides with Path of Radiance/Radiant Dawn
Greninja coincides with XY
Robin and Lucina coincide with Awakening
Corrin coincides with Fates
Incineroar coincides with Sun/Moon
Only Chrom and Marth break this trend.
Most recent FE game when Marth was added was Thracia 776.
As for Chrom, Most recent FE was Shadows of Valentia.