I didn't realize facts needed to be explained.
At least that's what people who constantly spout "Spacies OP" seem to show.
I don't really find spacies themselves to be absolutely OP from their skillset alone, but their 12 years of developed meta game puts them far beyond any other character. They are really figured out in a good way, standard melee players need to be WAY more technical than PM players because to win melee you need either 1. good reads 2. safe approaches or 3. more inherent pluses than your opponent.
The thing is that by playing textbook, "good fox." You are taking care of both 2 and 3. Fox is good because of little things, little things that ANY character could currently have. Things like knowing weak nair flows into other moves at certain %s, knowing exactly how + things are on shield and how he can safely apply nair > shine shield pressure. It is just a TON of little things.
If Fox wasn't in any prior iteration of the game and new to us, people would be like hey upsmash is strong, seems like upthrow to uair is pretty good, this shine thing is fast, but what do I use it for? It's just that a melee player can just crush with them by playing them solid against 100% of the characters in PM, but it is only possible because of how known they are. There is a correct use of them unlike any newcomer in PM.
Roy could be freaking amazing, Olimar could be top tier. It's all about discovery. People still find new janky once in a lifetime use stuff in Melee, but they will still learn it just incase the situation happens and it's flashy. PM players tend to be more open to change being that the meta game is so plastic, it isn't inherently a bad thing, but it becomes bad when people WANT change to fix something they don't like, AKA Fox.
I don't even know how Fox would be changed without unfairness. I would really feel for Melee players who do enjoy Fox and don't play him because he's broken. PAL modifications are the only acceptable bet imo because the developers put those in place after seeing what Fox could do. Even if you weaken upsmash, or hurt Upthrow uair good Fox will continue to wreck PM.
TL;DR NOTE: It may not be that Fox is too good, the other characters may in fact be better, but are not nearly as developed yet. Say no one changed, I believe PM characters to be so good it would be N64 esque in 10 years, in how these same current characters will have 0 to death combos on EVERYONE.