Phalanx systems are awesome and proven effective in the past. But they were designed in the 70s, based on a gun from the 50s, and deployed in the 80s. Are they still going to be effective against a swarm of modern hypersonic missiles? I don’t know, but if were wargaming, I’d rather be on the side attacking with hypersonics than defending with 20mm cannons.
they’ve mostly been replaced by rolling airframe missiles, IIRC.