I think that the AH conclusion might be that the OTL Whirlwind shows that a purpose built design as a fleet defence/strike/reconnaissance as a light twin engined aeroplane could have subsumed most of the roles that OTL required three types. However, the Blackburn Firebrand is an awful warning of how it can go horribly wrong.
I just looked up the Firebrand and dear lord. Its like a catalogue of how everything can go wrong. The UK really couldn't produce a truly decent naval aircraft in WW2. (See also the Spearfish which was also a steaming dogs egg.)