I have often wondered how to justify multiple platforms filling similar roles, great for whiff but not much good for real life. What I was thinking was, in particular with the light fleet carriers and their limited space, that the fighter selected for each air group/wing would depend on the other aircraft. For instance I imagined a Merlin group, a Griffon group and a Centaurus group, or perhaps a long range strike group with Sea Hornet, Sea Mosquito and/or Sturgeon, a tactical strike group with Fury and Firebrand/Firecrest (or Anglicised Skyraider etc.) and a sea control group with Seafire, Firefly (NF & ASW), maybe even an ASW version of the Seagull.
For the MB5, Fury and CA-15, it could perhaps be even simpler with the MB5 and the CA-15 being tailored to complement each other, say one as an interceptor and the other as a fighter bomber or escort fighter.