The IMC rating is just an IR with 15 hours of the training.
The way I see it, an IMC rating gives you enough training & experience to fly under IFR without killing yourself; an IR rating gives you enough training & experience to fly in Class A without inconveniencing other users of that airspace.
I understand that in the UK Class A airspace mainly comprises of airways. This is typically the easiest part of an IFR flight. You learn to fly straight and level before doing more complex maneuvers.
Therefore it's absurd to have an IMCR that is essentially an easy-IR with approach privileges and just 15 hours of training; and then an overkill IR with 50 hours training and crazy reading material which just gives you the
additional ability to fly in such airways.
IMHO the IMC rating shouldn't have given pilots ANY privileges when it was created. It remains a good course though. The invaluable skills taught by the course should be used by VFR pilots in an emergency to get them safely back down to the ground.
What's good news is the FCL008-IR coming soon. It should have been there some 30+ years ago.