I think it may have been 2Donkeys who wrote about some of the advantages of an IR over an IMC rating in terms of workload on a flight just within the UK...
(Assuming we are in an aircraft under 2t for sake of simplicity.)
With an IR, planned IFR: take off, maybe at an uncontrolled field, join CAS, single squawk (usually alloted whilst you're on the ground), seamless handovers from controller to controller until destination or you leave CAS to land at perhaps another uncontrolled field.
With an IMC rating, planned IFR: take off, try and get a service of RIS or RAS assuming controller workload permits and/or technical limitations don't prevent it, try and be passed from one LARS to another but often have to free-call and go through the whole "pass your message" again, assume you may have to avoid any class D zones in your path (you may not have to, of course) multiple squawks along the way...
That's why a lot of IR holders think it is easier
