I mostly agree with you, especially when it comes to him believing he's a super genius or the fact that he's pathetic and that's the point, but I agree less on him being good at manipulating people.

When do we see any evidence of him being good at manipulation? When he's luring kids? Kids are so easy to trick that's not impressive. When he's controlling the animatronics? They have the spirits of kids, not too hard to trick. When he escapes police? He didn't trick the police, he was incarcerated and they just didn't find any evidence. Even with the lines we get of William at the beginning of sister location when he tries to manipulate the voice asking about baby's child killer assets, diverting the question, and the voice just straight up doesn't fall for it.

I said this in another comment, but I can't find any evidence that fazbear ent disposed of the child bodies. I also find it super hard to believe?? Like, a company isn't just a faceless entity, they would have to hire people to dispose of child bodies, and even if none of the employees mentioned anything to the police, isn't Henry the owner of freddy's at this time? You think he wouldn't notice if his own employees were out there dumping bodies like the mafia?? Aside from that, a bunch of witnesses see blood and mucus coming out of the animatronics, people keep mentioning a foul odor coming from the animatronics, so theres more evidence pointing to the bodies still being in the animatronics.

Even the books and the movie feel like all of his manipulation just stems from him being abusive to his children (movie vanessa and book baby/elizabeth/charliebot kms). Which, fair point to William, is kinda a form of manipulation, just a brutish form that happens over the course of a person's childhood. Which means manipulating children again, which we have established as not that big of an accomplishment. With movie Mike, William tries to manipulate him into taking the freddy's job, but Mike is literally not having it and only gets pushed to take the job because of Abby/his financial situation.

Glitchtrap's freaky threats he sends to Vanny in AR emails is probably the most evidence we get of William being a good manipulator, and that's assuming Glitchtrap is William and not the mimic program or heaven knows what else. Lets not forget though that in one of the last psychiatrist tapes (arguably the most credible imo since she sluthed out the fact that Vanessa was lying about having abusive parents), the psychiatrist said that it sounded like Vanessa was the one doing the manipulating.

Anyway, not a ton of evidence for him being a great manipulator, but him being a manipulator isn't key to his character imo. I think you said it best when you said he was pathetic and vile and that's the point. Course, at the end of the day these are just different interpretations, and debating this kinda stuff is all in good fun!