This was I think also what was envisaged when the EU first wrote free movement into law -- general mixing, rather than one-directional floods.
But my point was that free-movement between near-peer countries seems like almost pure benefit. And this was where the EU started, knocking down walls in benelux... you would struggle to get many people upset about that.
Integration all the way to Romania etc. is more recent, really quite a different thing. The hope was for rapid convergence, and the evidence is mixed I guess.
I do not disagree with your claim about near peer countries.
Granted I acknowledge that has potential to be messy in reality without a whole lot of work to get a framework - let alone one that would be accepted. Perhaps some sort of "social service fee" minimum for benefits in taxes paid to prevent free rider issues for instance.
1. https://www.eff.org/deeplinks/2018/10/effs-letter-eus-copyri...
Spain isn't interested in getting an American immigrant just because one of its nationals moved to the US.
Its going to be a infinitesimally small fraction compared to the number of people from those regions that want to work here.
For really dodgy areas not soft postings like UAE / KSA you also get a premium. I remember a colleague who was on +80% for Angola (he got robed twice on the trip from airport to town)