Admittedly I didn't read through the whole post, but I didn't need to in order to agree. I never got the impression that Vernon was ever abusive or controlling towards Petunia and there's nothing to that effect in the books either. Fact is that Petunia married Vernon partially (or even fully) because he was basically as ordinary Muggle as ordinary Muggles came and Petunia wanted the ordinary. She wanted that a lot. If Petunia felt any differently towards Harry and her sister she would've stood up for that earlier. She wasn't a doormat. She was petty, close-minded and jealous but she wasn't a pushover.
All I can say for Petunia is that she did in some way at least respect Dumbledore, even if it was mostly out of fear or obligation. "Remember my last, Petunia." Then she spoke up and Vernon listened to her immediately.
When it came to Harry Petunia always called the shots. It means that she was the one who treated him poorly all those years too - if she had held Harry in higher esteem, Vernon would've done so too. He wouldn't have treated his wife's nephew so poorly for no reason otherwise.
Strangely enough, Petunia must've confided in Vernon at some point that Harry came from "that" side of the family and Vernon must've been able to accept it and he remained married to Petunia despite that. His love for Petunia was real. It actually makes you feel a bit sorry for Vernon in a way, the simple Muggle man who was quite happy selling drills and he had to get caught up in all of this.
So yeah, I agree! The way Harry was treated as a kid was definitely down to Petunia. If she had held Harry in higher esteem, Vernon would've definitely done the same.