He doesn't have sadistic tendencies for one
He definitely has sadistic tendencies, arguable on if they're more or less than Edwin's (since we don't get to see all of Killian's encounters and inner thoughts. His treatment of the girls in the club (often insulting and demeaning them) plus the meta knowledge that you get a point with him by stating you have a fetish for treating a woman like an object during Never Have I Ever is a big indication. His story about how he approached his maid Alice was also heavy on domination and sadistic dialogue, "With a little prodding, I even got her to admit I was fucking her better than her dead husband ever did." We've not seen him get physically sadistic, but that's only one aspect of sadism.
This I can see going either way, when compared to Edwin, we don't know how often he sleeps around. Given what we know though, he's cheated on Mina multiple times with Edwin walking into one such encounter. Inside the club he's a willing participant in the activities. Killian is absolutely a whore. More or less than Edwin though, I think Killian is worse, but definitely debatable.
I agree on this point, although I don't fully blame Edwin. He's in the process of discovering himself and his sadistic desires, so I feel his reactions are genuine, but he's not self aware. Of Killian's many flaws, he's not a hypocrite and open about what he feels and does in regards to his sexual tendencies.
He's also totally fucked up in the head when you consider that he watches his mom doing porn and all of this supposedly serves as moral compass to him. I mean, WTF? He was also joking (or not joking) about fucking Ian's mother (regardless of our choices), something you won't see Ian doing (he respects Victoria too much).
Killian has different issues than Edwin. Edwin's viewing of him mom's porn tapes is definitely fucked, but it's not clear yet if it's sexual or just as a self-flagellation of sorts (reminding himself he's only where is is now because of his mother's sacrifices). Killian won't joke about fucking Victoria, but that's specifically because he respects her and Edwin too much, he'll do things like that to other women. Again, that line "With a little prodding, I even got her to admit I was fucking her better than her dead husband ever did." is pretty damning.
Ian is a really good, loyal friend
Absolutely, very few would disagree that Killian's loyalty to Edwin as a friend is his best feature. Edwin isn't as good of a friend in return, but that does happen when friends start drifting apart in life (particularly during collage years). I would counter this point though by stating that while he's a good friend to Edwin, he's been a poor boyfriend to Mina so this level of loyalty seems to be solely for Edwin and not to all his friends.