A target with a 300mm frontal diameter, capable of evading at 10g, is expected to require 6 rounds to achieve a P_hit of 0.5 at 200m range, based on the parameters of your typical Phalanx CIWS. Said Phalanx weapon system might fire a burst of 1s duration in such an engagement, which is 75 rounds.

For a missile engagement, that's a problematic number, but for a drone that's probably only moving a few dozen m/s and carrying a small payload, it's an entirely satisfactory engagement.

Phalanx is an early 1980s weapon system. The Army is going to be fielding directed-energy SHORAD systems next year, equipped with 50kW lasers.