As Vapour says, the T42 isn't at her best in the littoral (where future operations will tend to be - and the most dangerous place) and only has two missiles on the launcher at any one time. Against a salvo of supersonic missiles, isn't the T23 with 32 vertical launch Sea Wolf better?
In a missile attack I would take a T23 any day. A T42 would depend on chaff and ECM for its survival. A T23 adds a very capable Sea Wolf system. The best solution is to have some FA2s in the area to shoot the missiles launch platforms down in the first place.