The Mandarin is a weird, mixed example.
Back when he was first introduced, he was basically a Mortal Kombat character in the Marvel universe. He had superhuman martial arts abilities, and ten rings that were basically just moderately powerful gadgets. He was the sort of character who would trap your feet in ice and then go off on you with the martial arts while you were partially immobilized. While at the same time he would have a scheme to conquer the world using science and armies and obscene wealth.
Over the years the rings got jacked up to ridiculous, boring, cosmic levels of power, doing things like turning a mountain into multibillion ton rock monster with a gesture. At the same time, though, the Mandarin himself turned into a jobber. His martial arts, science, wealth, and strategic scheming all fell by the wayside, and he kinda turned into one of those lesser Herald of Galactus types, the boring ones who pop up for one issue, use their powers in a stupid way that is only a threat because they are cosmically powerful, and then is promptly disposed of.
So they overpowered the Mandarin's rings massively, while nerfing the hell out of all of The Mandarin's personal abilities.