I think you're mixing together a few different things here. You don't have to like Revengeance, but "I don't know that guy" doesn't really tell me anything about whether Raiden's character development was good or bad.
And the "he's a cyborg now" part is a little off. Raiden was already a cyborg by the end of MGS4, before Revengeance. His transformation didn't suddenly happen because Platinum made a hack-and-slash game. It was already part of his established character.
Platinum developing Revengeance also doesn't make it somehow not Metal Gear. Kojima didn't direct it, but it was still made as a continuation of Raiden's story within the Metal Gear universe. You can dislike the genre change, but "Metal Gear isn't a hack and slash" is more of a preference about the gameplay than an argument against the game or character.
And the sales/meme point actually supports what I was saying. Raiden became recognizable in his own right. Calling him a meme isn't inherently negative, but it doesn't establish that he's inferior to Snake. Snake himself is extremely memetic, and Metal Gear explicitly plays with the concept of memes as a form of inherited information and expression.
I also find it strange that you say you "pity what happened to him" and then treat becoming a cyborg and becoming colder as though those things inherently mean his character got worse. That's another value judgment, not an objective description. Raiden's transformation is part of his character's development.
And I'm not defending Raiden simply because he's my avatar. I'm pointing out that your framing keeps reducing him in relation to Snake. You prefer Snake, that's fine. But "Snake is cooler" doesn't establish that Raiden is a failed character, and "Raiden is a meme" doesn't establish that either. In fact, the fact that Raiden became an independently recognizable character undermines the idea that he was merely an unwanted replacement for Snake.
