Most of the people with a problem with someone living with the name, is someone close in age. When you name a child for an older generation, like a great-grandfather, it is honoring that person. And considering the support Philip has given William, especially since his mother died, that would be a great honor. I still remember Philip walking with the boys during Diana's funeral. He didn't like Diana, thought she had tried to ruin their family, but he walked to support his grandsons on what was likely the hardest walk they will ever have to make in life.
Choosing a name for someone of the same generation, isn't really an honor. It almost seems like stealing their name. I guess you could argue Kate was naming him for her brother, but I don't know if her and Jimmy boy are so close, she'd name a son for him.