Vindicator's heel turn was poorly done in the Alpha Flight mini series a few years back by Van Lente and Pak. She was under the influence of brainwashing by the Master of the World the entire freaking time. I would be fine with that if she was still in character for at least some of the mini. What's worse is that in the first issue Mac comes right out and asks if it's brainwashing or if she's an alien after she attacks him, and she says 'No.' In retrospective, a line like that is too bare-faced to take seriously.
Just saw these, and it was slow-burn. Like Primetime Harder said, it starts with him having turned evil, but it's not until several issues in that you actually see what broke him. Even after that, you learn what pushed him to the edge over the course of years, and it isn't until the final stretch of the book that you find out about his origins. If you're curious, I'll give a basic description of his background below (minus the origin, because c'mon, the whole series builds up to that).
spoilers:end of spoilers
Plutonian was born with a full set of powers similar to a certain Kryptonian's, but unlike Superman he never gained enough discipline to be able to control them unconsciously; as a result, every second of his life was a constant struggle to avoid literally breaking the people around him--a struggle that ended in failure more than once. Not being lucky enough to find a Martha and Jonathan Kent, he was moved from foster home to foster home, each set of parents either being terrified when they learned of his abilities or quickly becoming such when they realized how little control he had. This engendered in him a near-pathological need to be appreciated and loved, a need he attempted to fulfill as an adult by adopting his costumed identity as the world's first superhero and using his powers to help the world. But even in spite of earning the adoration of the people, as well as the respect and friendship of his comrades, and managing to convince even his bitterest enemies (and quite possibly even himself, to an extent) that he was motivated purely by altruism, he was always psychologically on the edge: some major incidents aside, he remained detached from those around him, his skin so tough he could barely feel the touch of others, much less experience any sort of meaningful intimacy; his senses were enhanced to a degree that not only was he constantly overwhelmed by pleas for help, he could pick out every single critique, crack and insult directed towards him on Earth, and every time someone lied to him he could always tell, whether he wanted to or not.
In issues #7-8 we learn the incident that pushed him completely over the edge:
spoilers:end of spoilers
A scientist, having heard of Plutonian and his comrades confiscating technology from an alien armada they defeated, demanded access on behalf of the Earth. The team agreed to ignore him, lest forces beyond anyone's control be potentially unleashed, but Plutonian went to him and provided him with a trinket onboard, with instructions to summon him if anything went wrong. But one day, utterly fed up with the world's demands of him, he fled into space for 10 short minutes--the first period of silence in his life--only to find when he returned that while he was ignoring what was happening on Earth, the device exploded: he perhaps could have done something, but instead a sonic virus was unleashed on a nearby town that horrifically killed hundreds if not thousands of children. He intended to keep it his secret shame, but associates of the scientist contacted his part-time sidekick Samsara and told the boy the truth, undermining his trust in his mentor. In a rage, Plutonian flew to the scientists' lab, slaughtering them all while screaming that it was all unfair, that after all the years and suffering he'd been through trying to earn the love of the people around him he didn't deserve to lose everything because of a single mistake. In the aftermath, knowing there was no returning to being a hero and whatever faith he had in humanity burned away entirely, he chose to give up any pretense of heroism and go all-in to continuing his rampage, the only reason he doesn't slaughter humanity right away being that he wishes to toy with them and inflict on them the pain he feels they brought him.
Buh-bye
And for me, it was the scene that, in ultimately solidified Superman's place as my favorite character, as I understood the first time the pressures that role represented, getting me to think about the character in a whole new way.
Seriously though, one failed and lost everything, the other was Very Sad because he had a dream his wife would have a painful childbirth and so killed all the Jedi in the galaxy. One fails hard by comparison, but I don't think it's the guy in the cape. Don't mean to antagonize, I just really don't see how you came to that conclusion.
What other reveal could there have been anyway? He was terrifying, sure, but given that the premise of the series was that he used to truly be a hero and became this, he was always going to have to have been broken hard.
Buh-bye
Kid Miracleman is my favorite "hero turned villain".