Looking at Norman Friedmans "British Destroyers" it seems we have a mind set based on WW2 - Frigates "should be around 1500- 2000 tons, Destroyers 3000, cruisers 6000 tons
The inevitable growth due to the size, weight & complexity for a "destroyer" soon takes us towards 7000 ton ++ - trouble is early estimates are always too small and too cheap.
We either decide to build to the spec (if they can ever agree on it - I mean - the T45 has no SS missiles
) or accept we're going to have what are really enhanced River Class patrol boats