Type 12 (improved)
This was Leander. It was built on the basic hull form and machinery of the Type 12 Whitby and Rothsay frigates, which were specialist AS and AA frigates.
Interestingly, the last batch Leanders ('broad-beam') were actually completed with different specialist configurations (Ikara AS, or Sea Wolf AA, and I believe that some had Exocet) in place of the Twin 4.5" turret, and many older vessels were converted during their lifetime.
So we went from specialist to general, then back to specialist.
After this, the Navy wobbled a bit. The Type 21 (Amazon) which was a commercial design, which was regarded as a poor as a result of not having sufficient upgrade potential built in, but then the Type 22 Weapon or Broadsword, which was a Navy design, and the later 'stretched' versions were so successful that some remain in service today. As I understood it, the extra space was not for additional weapons, but for Command and Control capabilities to allow these vessels additional radar and tactical control facilities to allow a conflict to be run from on-board.
Looking back, it seems strange now to consider that the Leander class ran to 26 ships. Nowadays, the entire major surface fleet is not much larger.
And the other thing to note is that today's destroyers are the size of 2nd WW cruisers, the frigates are the size of flotilla leader destroyers. There are effectively no vessels in the small frigate/corvette category, as these do not have full ocean-going capabilities without sacrificing either speed or weapons for endurance.
In reply to everybody saying that the modern warships are armored, that is not really the case. Whilst they do have survivability design features, a single missile or largish bomb will actually take a frigate out, and they would suffer quite badly from shrapnel damage from a near miss. What they do have is the ability to operate in nuclear or bacterial contaminated fields of war (so called ABC, Atomic, Bacterial or Chemical), and the Type 45 destroyer is intended to be a 'stealth' ship, with surfaces and water sprays designed to scatter radar, to make it look smaller on radar than it actually is. Imagine how large a container ship, with large flat sides must look.
These features are most comically illustrated by the so-called Kryten turret (Mk. 8 improved), which looks, naturally, like Kryten's (from Red Dwarf) head.
In addition, a warship must be able to move at least as fast as the rest of the group it is with (and with allied Navies), and to be able to react rapidly (which is why they switched from oil fuel steam turbines that had a startup time measured in hours, to Gas Turbine and/or Diesel, to allow a ship to be underway in a matter of minutes). Keeping j-fuel safe in combat is MUCH more difficult than keeping heavy oil fuel, which requires more design work.
And Lewis's ill-informed musing about carriers being able to protect themselves does not take into account amphibious warefare vessels like HMS Ocean, which do not have all the trappings of a full carrier.
Putting it bluntly, frigate sized ships are much more cost effective and useful in any number of different, and possibly un-expected environments than helicopter-carrying RFA's.
So Lewis. 3/10, could do better.