Before missiles, why were jet fighters deemed to be so much better than WW2 era fighters? Both could only shoot each other down with guns. A higher top speed can mean you can choose your engagements and be like "eh, nuts to this" if you are in an unfavorable engagement. If you're escorting slow moving bombers or transport aircraft, I don't see how being a jet fighter helped that much. Later bombers could move at faster speeds and would outpace an old fighter and later fighters could shoot down a propeller plane easily with a missile (when the humidity didn't mess with the electronics... hey let's do all the testing indoors it's not like it rains in Europe), but I don't see why early on people didn't think "these fighters will be the future" as opposed to "the future is now the present, these shiny new jet planes are the king of the skies"