Sounds like sour grapes (should be a fine whine by now due to age).
Other than not having the ships for an invasion, the RAF was the key factor. What does that guy think...that if the RAF was defeated, a navy without air cover would have held off the germans? I think we know how that type of battle pans out.
If the RAF had failed, and Germany gained control of the skies, the RN would have eventually ceased to exist, its fuels depleted, and invasion would have been imminent.
Im just an amateur historian, but I think this guy's dad was old navy, and he grew up in a household full of contempt toward the RAF.