5 Mt is huge, and far bigger than the warheads of most modern nuclear weapons. The one you show is fairly representative of a single modern warhead. Nowadays, and for many decades if you want a large area of effect, you use a MIRV vehicle and pepper the target area. This gives you wide coverage for fewer total megatons and a more compact and flexible weapon system, and hedges your bets in case any of the warheads fails or is intercepted.

In fact big bombs were an early trend for two reasons. One was that the delivery system was expected to be bombers dropping one or a very few bombs with mediocre accuracy and so you wanted maximum destruction from each delivery. The other was that they were worried bombers wouldn't be able to get directly over some targets due to air defences, so you'd drop the bomb short of the target and use the massive area of effect to cover the remaining distance for you.