I know you weren't talking to me, but I played both routes at the same time, seeing the differences, and these were my impressions of the MC through both paths:
Seduction: MC realizes that all the people he blamed for the things that happened to him don't actually have the blame; they all had their own problems, and some of them were MC's own fault, like Emily bullying him and ignoring him because he never played with her and ignored her too in the past, so she got fed up. Or Viktoria bullying him because he broke his promise to her and separated from her despite them being best friends at the time. He grows out of his resentment, decides to fix his relationships, tries to prove to them that he can love all of them, and goes for a healthy path (although he is still very narcissistic since only someone like that can think that they can pull off a harem).
Corruption: MC doesn't learn any of that; he instead rationalizes his hatred to justify his own actions.
MC's thinking: "Oh yeah, me blackmailing and raping my crush is totally justifiable because she never realized that I liked her. Like, she should have known even though I never told her and should have picked me instead of the boyfriend that she had since before she even met me, so blackmail it is."
OR
MC's thinking: "Oh no, fuck whatever Alyvia wants to do. I don't want her to lose her V-card to anyone but me, so I'm going to send blackmail material to the bitch that has been tormenting her all this time, screwing her at levels that may go way beyond anything she ever did to me, so long as she remains a virgin for me."
Yeah... totally healthy behavior. In the corruption route, he never grows; he gets worse; he becomes a controlling psycho.
Just look at Viktoria and Catherine's paths:
-Seduction: Loving relationship.
-Corruption: Toxic relationship.
With some girls, like Stephanie, it is less noticeable until you see that seduction has a "lovemaking" scene, while corruption has a "choking the hell out of her" scene. MC is just darker and sometimes unhinged in corruption path.