From my perspective, the reason Pokemon or Mario get 'a pass' on having a large rep count is that the characters all pretty much play differently (Obvious exceptions to the 'echos' like Doc and Daisy). Half the FE reps are nearly the same character with a slight gimmick to differentiate them. Lucina, Roy and Marth are virtually the same character, move for move, with small tweaks to properties in their moves to set them apart. Chrom is a poor amalgamation of the trio and Ike, one of the remaining few who is wholely different. Then there is Robin and Corrin who are distinct from their peers.
The Pokemon all offer different play styles entirely (Sans Pikachu and Pichu. Some could argue Lucario and Mewtwo but their similarities end with floatiness and ball tossing). So though the series has lots of reps, they offer a multitude of variety in how they all play.
Mario series also does the same. Mario, Luigi, Peach, Bowser (Wario and Yoshi if we want to just roll it all up) all completely different.
If FE characters continue to come, I won't mind. Provided they actually differentiate themselves more. Which is why they really aught to just stop using the same sword style so they can't unwittingly (or purposefully) fall back on recycling moves/animations.
I care more about unique additions more so than 'oh, another X franchise character?'. The next pass could all be FE characters and I'd buy them if they all were distinct and fun.