While I do feel a bit disappointed that Oz wasn't a yandere character, honestly I think it was obvious given how the plot turned out. I think it wouldn't really matter much since if Oz really was a yandere, then it would, in a sense, undermine MC's conflict. The entire thing is that MC was betrayed and falsely accused by someone they trusted genuinely, and if Oz was a yandere he would either manipulate or imprison MC but with how MC is designed it would just add on another layer of conflict that doesn't feel necessary.
MC is very independent and knows their goals, they're very determined so Oz just being their partner in crime and watching MC fall further to madness of wanting to get back at the traitor would make much more sense than if Oz was a yandere (and I like dark MCs because of the unreliable narrator and twists of perspective). Either way, I'm looking forward to how the plot would progress!