Come on, this isn't a redundancy to increase your range when you fly too far out, it's a redundancy in case the 2.4g spectrum is jammed, packed with interference or just drops outWell, that sounds strange and depends on the reason control is lost, because when link is lost on 2.4GHz, on 5.8GHz is probably gone from longtime already.
That's one reason because video is usually on a shorter wave length: when video degrades there is still full control and it's time to come back.
Ric