One, large, central weapon against a swarm of hundreds of small ones? It's a deadly assumption that an entire swarm would come from one direction, for example. Or that it would appear all at once. I'm sure volumes will be written about the strategies yet to come, but if what we've seen in the 20 years of occupation of Afghanistan and Iraq is anything to go by, asymmetric warfare is very effective at tying up resources.
Watching what the twichy youngins do with FPV drones gives me the heebiejeebies -- this has already transferred to battlegrounds in Ukraine, with some serious impacts (no pun intended).
The problem is that drones are cheap and easy to slip around defenses. The other issue is weapon system reliability... the US military expects an extraordinary amount of reliability from munitions / weapon systems and they are supposed to be near 100% reliability. When they launch a missile, it's unacceptable for the missile to not launch.
The Coyote[1] is an interesting counter UAS concept and could be much more cost effective solution.
There are some German AA guns that have been used for counter UAS, but their export laws are a fucking nightmare to deal with if you ever want to sell, give or trade those systems later on.