I think you need to give it some more time. It sounds like he feels less useful with her because she needs nothing from him, whereas your first two needed him to be fully involved because they were less placid babies. My DH took months to bond with my DS2, and the same again with my twins because I did all the day to day caring and didn't need much from him other than distracting the older children, and from friends I have been told this is not uncommon. He will grow to have the same attachment with her as he has to your others but it may happen at a different point in her development. Be patient and I'm sure it will happen.