I wonder how many nations need long range for defence? Of course offensive wars such as invasions of Iraq and Afghanistan are different, but most uses for defence should happen relatively near to border.
Defence is not that different from offence. An offensive task such as destroying enemy artillery behind their borders or their service routes is an effective way to defend. If the enemy has nothing to attack with, then defending is a lot easier.
I think that would make sense for some missions like air superiority but not others like a deep strike into enemy territory. For the former we already have AWACs that perform nearly that role while also being big flying radars. For the later I think something like the F-35 might actually be the best solution, though with a number of robotic subordinates.