The problem with Ridley is trying to balance him.
It's really hard to maintain a balance with his fast air speed and attacks, fierce power, and heavyweight status Ridley is well known for; as it could potentially break enjoyment of the game if he's unbalanced. Pig Ganon doesn't have a sheer problem with balance, he's not known to be a fast OP character in his games like Sephiroth (best example I could provide) that would require heavy balancing while staying true to his character.
Ridley's not even that heavy. Or that big. He's fast and strong and can fly, in addition to plasma breath, claws, talons and a prehensile stinger-equipped tail. But he's not a heavyweight brute.
That may sound imbalanced on paper, but that's to wantonly overlook the fact that there are plenty of other characters that are similarly balanced in Smash whilst staying "true to character".
Enormous brute that's almost always invulnerable to everything except external forces (lava pits, explosive mines, etc)
Can fly indefinitely in addition to everything else he can already do
Is literally a deity
Can potentially be fast, powerful, accurate and have damn good luck
Nigh-indestructible, can and does obliterate planets on a regular basis
The fastest thing alive, should logically be ripping through opponents like they're tissue paper
Can KO enemies with a single hit (PK Flash)
Fast, strong, has access to a near-infinite repertoire of powers, can crush enemies with a single jump
Super strong, super fast, super durable, super handsome...what
can't he do?
I'll leave aside such characters as DK and Ganondorf since their "true to character" depiction is sketchy, but that's still a pretty solid list of characters whose innate powers have been balanced to fit into Smash. Arguing that Ridley is "unbalanced" because he's fast, strong and can fly is just looking for reasons to be spiteful.
He's almost never shown fighting on the ground, and for good reason: he sucks at it. So make him the anti-Mac, or a bigger and scarier Jigglypuff: awful on the ground, a terror in the air. Make him a glass cannon, fast and strong, but he breaks with a single punch.
None of this is new. Claiming "it won't work because reasons" isn't a sufficient validation for why he shouldn't appear. Offer alternative perspectives. Determine how to resolve these issues rather than seeing them as insurmountable stumbling blocks.
It can, but then it wouldn't stay true to the character, which is something Sakurai talked about before.
Now you're just parroting Sakurai to prove your point.
Almost nobody in Smash is portrayed with absolute accuracy, and I will provide a detailed list if you would like me to.