High-end air defence and neglected cheap threats

What has been the biggest mistake in shipboard anti-aircraft defence?

The criticism is that pursuing advanced threats has left ships without enough fitted systems to counter cheaper weapons.

An increasing focus on defeating advanced weapons is criticised for leaving cheaper threats inadequately covered. Lower-cost weapons can appear below the level for which expensive defences were acquired. Ships may then lack suitable systems already fitted to address them. The missing provision for cheaper threats is the recurring design criticism.