In fact, to prone doesn't take that much time in real life. Like half a second, the reason why it would take you 4 seconds is because you don't want to hurt yourself by doing so. But when your a soldier, your equipped with protecting equipement for your wrists and knees. So you could actually just dive for the ground. But of course, diving like in Battlefield 2 early patches is kind of dumb.
To prone would add a great experience to the game play, that would be my opinion.
Anyway,
Have a nice day!