Nah, I’m heavily doubting Loki as a villain. He’s far from the first character to have a bad reputation, but still end up a good guy. That’s the background for most of the Strawhats tbh.
Look at what we have with Loki
-before the arc began, we are told he was in love with Lola. If that is true, then that’s a point in Loki’s favour. Lola is ugly, but she has a good personality. It’s suggesting that Loki cares not about the surface, but about the personality.
-Gerd says that Road is more of the shame of Elbaf than Loki is. That’s the first mention of him in the arc. I find that an odd thing to say. Road isn’t really a bad guy, he’s just a bit of a freak. So to me, immediately comparing the supposed Prince of Darkness to someone else as worse, and that other person not really being so bad... doesn’t set up Loki as someone wholly bad.
-His main sin is that he killed Harald. Seems pretty clear that with the latest chapter, the Celestial Dragons visiting Harald’s grave and the lack of witnesses, that there’s far more to this story than meets the eye. All the other stories of his past remind me very much of Oden’s reputation as a youth. I doubt that Loki’s pranks are him trying to do good, but I do suspect it’s just him doing things that get a bit out of hand.
-he’s judged from birth the same way Hajrudin is, but for a different reason. There’s a prophecy about him- Loki can’t help that. The year he was born was a shitshow for Elbaf- Loki can’t help that. Seems to me that a target was painted on his back from the beginning. Might be that he’s just loving up to the reputation created for him
-he’s friendly with animals, and Luffy becomes friends with those animals as well. The animals are willing to fight for him. That’s not a trait I think Oda will associate with truly bad guys.
-the whole thing where he gets angry when his mysterious freind says that Loki’s angry words just hide his kindness. That’s shouting that there’s some misunderstood parts of his personality, and a lot of what he does is covering that up
-like Kid, another Tsundere bad reputation ally, he can tell the true shits of the world are the Celestial Dragons, and that’s a depth he won’t sink to. Note that Loki does want to be free... but that he still refuses to join them and help them take Elbaf. So Loki has some moral standards
-the entire thing about Luffy, Zoro, Gaban and freeing him. It’s one thing Luffy, being a cheerful and naive (but also good judge of character) trusting him, but Zoro and Gaban also really didn’t take much convincing to release him. Now, Gaban seemingly actually knows Loki. If he’s as evil as Elbaf thinks he is, I doubt he’d be cheerfully letting him loose. Which he basically did. And Zoro is far more suspicious than Luffy is, but he’s went through with it. After all, Zoro has first hand experience that being locked up for being a demon might not be the full story.
Doesn’t rule out him and Luffy having a fight at some point, but having a fight does not make him the main villain.