Hmm, interesting.
Could the same layered approach then not also be achieved by only missile launchers?
Use 1 type of Anti-missile fire control that has 5-6m km range, but use different range settings in the combat menu?
For instance, a simplified example:
You have a PDC with 3 missile controls, that have a max range of 5-6m km, and a resolution 1..
It has 3 (size 1) missile launchers, each linked to one of the fire controls.
Now, in the combat settings, you set the "Max PD range in 10k units" to 600 for one launcher, 200 for the next, and 50 for the last.
You could use three types of missiles for them, trading fuel for agility at each layer.
I guess that would be have economic benefits as well, as there is less chance of wasting missiles on overkill shots (if you calculate things right, and make sure that each layer's salvo will intercept incoming missiles before they reach the next layer's range.
A bigger economic benefit would be, that you do not need to put effort into researching beam stuff, and concentrate on getting *really* good missile power.