Only Speed cannot help in it.
Its a trade-off actually. That's why better to have both kind of missiles in your inventory.
The supersonic missiles are designed to beat ship's air defenses with sheer speed. But it tends to be detected far earlier.
The subsonic missiles are designed to remain undetected until its too late. Only CIWS/PDMS may respond at the last moments.
Detection is the key in interception. Sub-sonic missiles have better capabilities to remain undetected:
- Subsonic ones normally have lower RCS, smaller / lighter then the supersonic.
- Very low thermal signature
- The subsonic missiles fly at very low altitude / terrain hugging. They just fly above the wave tops. Something which you cannot achieve with super sonic missiles as of yet. They can fly low but not as much as compared to subsonic ones.