So I think this has already been said, by @ChrisGiles_ but I'm going to say it again. The MAC recommendation to have migration rules that don't discriminate by country of origin are not to be taken in isolation.
Because making that choice has consequences for our other economic relations. Obviously, if we have such a rule we exit the single market, unless we have FOM for all individuals in and outside the EU.
And that is not just a consequence of arbitary rules of the single market. The single market itself arguably depends on the four freedoms - particularly in services. But also in light of nationally dispersed supply points and nation state border criss-crossing supply lines.
If making migration non-geographically-discriminatory involves exiting the single market, then this is NOT a good idea, given the benefits that that membership confers [and presuming FOM globally is undesirable or infeasible].
It could be made a better idea by reforming the single market to curtail or eliminate FoM. But that would also reduce the benefits of being a member of that market, which depend on FoM to some unknown extent.
It also should not be a cause for alarm that impacts of migration differ across regions / sections of society. Most policy choices are like this. Redistributive taxes and subsidies are there to sort these things out, albeit imperfectly, and with other political constraints.
'Oh, we can't have free enterprise, because the benefits are felt heterogeneously.'
This is obviously nonsense. We encourage free enterprise, which has aggregate benefits. And redistribute heavily as not everyone can / should be involved in it directly.
