Have you really only just found out about the legacy UK CPL(A) and ATPL(A) privileges, DFC? It's a pretty fundamental part of the whole sorry saga.
The excuse for the CAA cock-up was that the JAR-FCL CPL(A) training 'was not the same' as it was in the days of CAP54. It must have taken them quite a while to research that piece of nonsense.
Nor will they pay for the adminstrative effort required to issue a 'free' IMCR to JAR-FCL CPL(A) or ATPL(A) holders unless it is requested at the time of IR(A) initial issue.
Your example of the Cat 2 minima is nihil ad rem. You cannot compare a 'recommendation' for the IMCR with an absolute regulatory requirement for Cat 2 operations.
Also, the excerpt you quote from Standards Document 25 does not state that applicants must adhere to the IMC weather minima quoted in the AIP, merely that they are 'expected to'....
The impact of the loss of legacy IMCR privileges if EASA requires all UK CPL(A) and ATPL(A) holders to convert to EASA part-FCL licences has already been made plain to the CAA on many occasions.