Ok so, this is wacky.
An important thing to note is that Raiden, knows about Mantis, knows what he can do and how he acts in a fight and so on, Raiden did multiple simulations of the Shadow Moses Incident, he knows about Mantis and technically has "experience" fighting and defeating him.
So that would imply he'd win? Yes but technically no.
It's important that while it was simulated, he was playing the role of Snake, he had access to what Snake did, which he doesn't have here.
Mantis could read and WILL read his mind, and thus know that Raiden has experience with him and knows how to win, so Mantis can work around that anyway.
The main issue with this is that, the way Snake managed to defeat Mantis, Raiden technically doesn't have.
Raiden lacks every ability or method that Snake was forced to use to defeat Mantis because everything else was completely useless. As it stands there's nothing on Raiden's profile that enables him to even land a hit on Mantis, beyond maybe a few stray shots like Venom sometimes pulled off (which he did via perception manip).
In context, Raiden, should, in theory, be able to overcome Mantis and defeat him with difficulty, but that's in universe, we can't say for sure if Raiden can empty his mind o̵r̵ ̵s̵w̵i̵t̵c̵h̵ ̵c̵o̵n̵t̵r̵o̵l̵l̵e̵r̵ ̵p̵o̵r̵t̵s̵ ̵ like Solid could, and without that, his only method of defeating Mantis is to make him see himself (as in, make Mantis see his ownn face), which he would be well aware of as being a weakness to Mantis, but that begs the issue, how in the actual **** is he gonna do that?
Snake could do that because there was statues of Mantis' face in the area that he destroyed to reveal the faces, for some stupid reason, that isn't the case for this match given it doesn't take place in a specific room on a random island in alaska, meaning Raiden would need to destroy his mask and have him see some sort of reflection which yeah he could likely pull off the reflection thing but the mask part? That's the whole sisue to begin with, even hitting the dude enough to land lethal damage (Which may as well be impossible as Mantis is gonna know all his moves and can avoid them).
honestly, I kind of want to vote Inconclusive, Peak MG2 Raiden knows how to beat Mantis and probably could in context, but by wiki standards we can't really say "yeah man Raiden could win because of this and that" when he doesn't actually have this and that that would enable him to win as it hasn't actually been shown in verse, even if he might have it or can maybe learn to.
By wiki standards, Mantis mind reads his every move, avoids everything, and just TK's and psychokinetically wears him down to death.
In universe, he probably just does what Snake did and does cool 4th wall or ultra instinct shit to gun Mantis down or bomb him to death or whatever else he can do with the small military arsenal and skills that he has.
So I wanna vote incon but if I HAVE to vote, Ill vote Mantis due to Raiden lacking the needed resistances that he'd need to get past Mantis with his toolkit he has access to f̵o̵r̵ ̵n̵o̵w̵ ̵a̵n̵y̵w̵a̵y̵
