Look. I'm chill. No disrespect to you.
Any disrespect is to Dark Pit as a Smash character choice.
There are certain literary/universal arcetypes that you can group characters into. And the Joker/Pit and Dark Pit/Batman comparison does not fit well together into these archetypes. Its a very loose comparison, and I only call it disrespectful because I have much respect for Batman and Joker as characters, and little respect for Dark Pit.
Dark Pit is a foil character, a doppelganger if you will, created in Pit's image to screw with/oppose/ be the "straight man" to Pit. And though he may have a stoic, cynical characterization, he's still a Dark/warped shard of the protagonist.
There is no "Dark Pit" without Pit. Which is why, I believe, despite whatever mannerisms that seperate the two, Dark Pit was better left as a palette swap.
Batman and the Joker may share elements within their origins, but neither of them caused the other, or was the inspiration for the other in their fictional timelines. If one of the two never happened, that doesn't mean the other wouldn't be relatively the same character. They effect each other certainly, but one's existence never depended on the other's. And sure you can say that Batman knocked Joker into the chemicals that changed him, but he was psychologically disturbed beforehand, and your argument is that Dark Pit is the Batman character, not the Joker character.
More relevant comic book comparisons would be Hulk/ Red Hulk, Wolverine/Daken, Superman/Bizarro. But then again, they'd all be appropriate palette swaps, like how Dark Pit should remain.