The IR is conducted in a single pilot aircraft which does not lend itself as well to multi-crew training.
I disagree with this assertion. I think that as long as the IR/ME SP aircraft has an advanced autopilot, then it is fine for role differentiation in MCC training.
But I agree with you that it is even better that MCC training is performed on they same aircraft as first type-rating - but this is not practical the way that training is currently structured.
I think that forcing students (who may not have any worthwhile IR/ME SP experience beyond their basic training) to do MCC on a completely unfamiliar type is a poor third.