Have to say Not a Boffin I do agree with you about the design of warships IMHO some of the Falklands lessons appear to have been forgoten. and a smaller calibre 20-30mm is multi purpose and better for stopping smaller vessels on the high seas a 4.5 being pointed at a foreign vessel could be more diplomatically embarassing than a 20mm oerlikon or 40mm Bofors.
The stealth design may lower the detectability but we must always plan for ships to be attacked and have the layers to defend themselves. The best the royal navy has at present IMHO is the T22/III. The 23's were a step backwards in not having a phalanx or goalkeeper system.