A British 1905 light cruiser

I thought that exploring what could have been done with a British light cruiser laid down in 1905 would be a good exercise. Such a ship would have certainly had coal-fired boilers and steam turbines. I don't understand the fixation on the 4in gun. Perfectly good 4.7in guns had been produced for many years and were widely used and had seen combat. At this date, there would have not been any side armour, just a protective deck. This is the Springsharp report:

GB/CL/1905, Great Britain Light Cruiser laid down 1905 (Engine 1911)

Displacement:
 3,658 t light; 3,787 t standard; 4,586 t normal; 5,225 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
 (436.00 ft / 428.00 ft) x 41.00 ft x (17.00 / 18.85 ft)
 (132.89 m / 130.45 m) x 12.50 m  x (5.18 / 5.74 m)

Armament:
      8 - 4.70" / 119 mm 45.0 cal guns - 50.00lbs / 22.68kg shells, 150 per gun
   Quick firing guns in deck and hoist mounts, 1905 Model
   2 x Single mounts on centreline ends, evenly spread
   6 x Single mounts on sides, evenly spread
      Weight of broadside 400 lbs / 181 kg
      4 - 18.0" / 457 mm, 20.00 ft / 6.10 m torpedoes - 0.865 t each, 3.459 t total
 In 4 sets of deck mounted side rotating tubes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Ends: Unarmoured

   - Torpedo Bulkhead:
  0.60" / 15 mm 300.00 ft / 91.44 m 17.00 ft / 5.18 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 3.00" / 76 mm 2.00" / 51 mm  3.00" / 76 mm

   - Protected deck - single deck: 2.00" / 51 mm For and Aft decks
 Forecastle: 2.00" / 51 mm  Quarter deck: 2.00" / 51 mm

   - Conning towers: Forward 4.00" / 102 mm,  Aft 0.00" / 0 mm

Machinery:
 Coal fired boilers, steam turbines, 
 Direct drive, 2 shafts, 30,308 shp / 22,610 Kw = 27.00 kts
 Range 4,500nm at 15.00 kts
 Bunker at max displacement = 1,438 tons (100% coal)

Complement:
 278 - 362

Cost:
 £0.357 million / $1.430 million

Distribution of weights at normal displacement:
 Armament: 117 tons, 2.6 %
    - Guns: 114 tons, 2.5 %
    - Torpedoes: 3 tons, 0.1 %
 Armour: 704 tons, 15.4 %
    - Torpedo bulkhead: 113 tons, 2.5 %
    - Armament: 115 tons, 2.5 %
    - Armour Deck: 452 tons, 9.9 %
    - Conning Tower: 24 tons, 0.5 %
 Machinery: 1,353 tons, 29.5 %
 Hull, fittings & equipment: 1,484 tons, 32.4 %
 Fuel, ammunition & stores: 927 tons, 20.2 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   5,076 lbs / 2,303 Kg = 97.8 x 4.7 " / 119 mm shells or 1.0 torpedoes
 Stability (Unstable if below 1.00): 1.18
 Metacentric height 1.8 ft / 0.5 m
 Roll period: 12.9 seconds
 Steadiness - As gun platform (Average = 50 %): 74 %
   - Recoil effect (Restricted arc if above 1.00): 0.36
 Seaboat quality  (Average = 1.00): 1.48

Hull form characteristics:
 Hull has rise forward of midbreak,
   a ram bow and a cruiser stern
 Block coefficient (normal/deep): 0.538 / 0.553
 Length to Beam Ratio: 10.44 : 1
 'Natural speed' for length: 20.69 kts
 Power going to wave formation at top speed: 56 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): -3.00 degrees
 Stern overhang: 2.00 ft / 0.61 m
 Freeboard (% = length of deck as a percentage of waterline length):
    Fore end,  Aft end
    - Forecastle: 20.00 %,  23.00 ft / 7.01 m,  22.00 ft / 6.71 m
    - Forward deck: 17.00 %,  22.00 ft / 6.71 m,  22.00 ft / 6.71 m
    - Aft deck: 48.00 %,  14.00 ft / 4.27 m,  14.00 ft / 4.27 m
    - Quarter deck: 15.00 %,  14.00 ft / 4.27 m,  14.00 ft / 4.27 m
    - Average freeboard:  17.04 ft / 5.19 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 203.3 %
  - Above water (accommodation/working, high = better): 129.9 %
 Waterplane Area: 12,110 Square feet or 1,125 Square metres
 Displacement factor (Displacement / loading): 121 %
 Structure weight / hull surface area: 67 lbs/sq ft or 325 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.92
  - Longitudinal: 2.00
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is extremely poor
 Room for accommodation and workspaces is excellent
 Ship has slow, easy roll, a good, steady gun platform
 Good seaboat, rides out heavy weather easily