Depends on the situation.

An example is the https://en.wikipedia.org/wiki/Battle_of_the_Shangani where 5 guns defeated a force of 7000.

However when both sides had the same capabilities, attack became very costly.

The point is, depending on the type of drone, the sheer cost of fighting them off is prohibitive with current interceptor tech (ie anti air missles). In fairness they were designed to attack targets 10x their cost, and take years to build.

For the USA specifically, they have a bunch of bases within range of cheap drones. This means that you need radar/sensor controlled chain guns, or moveable nets to defend cheaply. Its almost time for barrage baloons.