[Alneyan]

The armour will be able to regenerate, what, perhaps 75 shield points in the current setup, less than what an extra APB would do (an APB takes the same space as a Shield Disruptor if memory serves, or the Shield Disruptor is bigger).

A vessel with 10 Crystalline Armour is immune to anything doing less than 150 damage points in a single hit (normal damage that is), unless using specific designs. In this case, a Shield Disruptor would have indeed been useful, as the regeneration can be very annoying. (There are other ways to deal with a Crystalline Armour however, but this is another topic)

Shield Disruptors can also be good if you are annoyed by vessels with a lot of shield generators. However, Shield Disruptors do not do enough damage to take down more than a few shield generators per hit, and you will need to close to range 2 or range 1 to do a lot of damage, so it does not go well with a "fight at maximum range" plan.