He, Falco, Marth, Sheik, Jigglypuff, and Peach - that dumb Down Smash -, Ice Climbers by virtue of dumb grab mechanics, and plenty more are broken in Melee. Meta Knight, Falco, Snake, Ice Climbers, Triple DD, and probably more because of chain-grabbing's existence were all broken in Brawl. Smash 4 has like what? Diddy, Greninja, and Rosalina at launch? Luigi after patch 1.0.4? And now... like nobody, but for some, arguably Rosalina, DK, and Sheik? Even then, they're pretty tame compared to Melee and Brawl's level of brokenness. If anything, they're just way too good compared to everyone else or have over-tuned options.
I'm on mobile, so I'm not going to go over everything, but to sum up how broken Fox is: frame 1, invincible on frame 1 Reflector used for gimping Melee's poor recoveries and setups since you can jump out of it and a 18% Uair that can easily be setup out of U-throw. Everyone has or can see high level Fox play and notice how dominating he is.
The gap between Fox and the other top tiers is so large, it's not funny. And people want more of this because unlike other fighting games, Smash never had to deal with balanced and unbroken characters.
It's still a frame 24 move that only has 1 active frame and with 41 total frames, it only has 16 recovery frames... That's like decent tilt recovery. Then again, Mario's Up Smash is kind of stupid at times too.