This is rather irrelevant but I don't see how the IMCR (no Class A) is sub-ICAO any more than any IR (with some other limitation say no commercial use and needs to have one's left goolie weighed every 6 months) is sub-ICAO.
If you take the IMCR and remove the fairly recently added "UK only" limitation, it is totally equivalent to a full IR - in any country in which Class A is either missing or not operationally relevant (i.e. all except UK and Italy, in Europe).
In terms of how the syllabus matches all-airspace full-IFR operational requirements (let's forget for now that the IR syllabus is woefully inadequate for real GA/IFR) the only really big bit missing from the IMCR is SIDs/STARs, and they require the amazing ability to ..... wait for it ..... READ the piece of paper with "STAR" in the top RH corner
It's all about the politics of
professional pilot status in Europe, which for historical reasons has become closely attached to the
IR. It should actually be attached to the ATPL (which is how it works in the USA) but Europe has structured the ATPL into a free gift to any fATPL pilot reaching 1500hrs with the MCC time etc. So, since the ATPL is basically a bogus thing over here for anybody with a RHS MCC job, they had to tie professional pilot status to something suitably elitist, and the IR is the only thing that's left. The CPL is a VFR-only exercise which "anybody" can pass, eventually, but by itself it is useless.