I think they benefited because Kate had a relatively normal family life and could bring that and adapt it to their circumstances. William and Harry bounced between the traditional upper class/royal childhood of Nannies and boarding school and only seeing family at set times to being swept along by Diana. Their attention was either feast or famine. There’s no wonder their views on parenting are a bit skewed.And not two children are parented the exact same way. Even siblings. You as a parent change, children are individuals as well. Personalities clash or compliment each other. What works with one, is not ideal for the other.
I think that Wilian had his own struggles to come to terms with his father. At least around George’s birth that was heavily hinted on. He was very open to seek out therapy and he found a second family in the Middletons. I wonder if they are close now, or just realised they had to build something new. If Wiliam has set his eyes to the throne and therefore goes along? The Cambridges were pretty clear about doing this differently and making different choices regarding their children. All without publicly pointing the finger on tv.