I said nothing about the sub-classes being represented, just the class overall. Also, the Royal Navy's official name of the 1936 Town Batch 3 subclass is Edinburgh, not Belfast.
The sub-classes would be alternatives at each tier, or at the tier below with a slight nerf as suggested here:
Can't upvote this enough; this would also work with the Crown Colony batch 2 (Ceylon) class.
Belfast, presented in-game after her 1956 post-Korean war refit, has indeed been removed as was Mikhail Kutuzov at Tier 8. And they were indeed widely considered to be OP in the right hands, although that was based on taking a solid design & adding a consumable - Radar for the Belfast & Smoke Generator for the Kutuzov.
Actually, Fiji only represents the batch 1 Crown Colony class; batch 2 were the Ceylon subclass, the Swiftsure class (of which only 3 were completed as designed - Swiftsure, Superb & Ontario (HMCS, ex-Minotaur)) were modified Ceylons, all with 3x3 152mm main guns & increased AAA over the Fiji subclass. Of the other four Swiftsures, Hawke was scrapped when 95% complete (including her Mk 24 DP main guns), Defence, Bellerophon (completed as Tiger) & Blake were of a different design and were eventually completed as the Tiger class cruisers.
Placing either Ceylon or Swiftsure in-game is problematic, they're best as either a T6 premium with 6km torpedoes or as a Commonwealth T7 (Ontario) with an ROF boost to compensate for the missing 3 guns.
The word you're missing is light & as the classes have a presence as a whole, I wouldn't claim they were entirely unrepresented - apart from Dido. Also missing are the RN CA's, which is a different subject.