Critiquing the EU on Worker's Rights
That is kind of how the expansion of the EU works: loss in autonomy and integration into EU institutions, commitment to EU values (human rights, democracy, market economy) and EU jurisdiction.
I would say the policy was a remarkable success. I regard myself as a EU citizen.
BUT: People will still move to the established economic power regions, the same as people from poor US states move to rich US states.
And you need man power to colonize something, with modern low birth rates this is impossible, British complain about polish plumbers, but they are not founding English neighborhoods in Poland (even though they could), the same as no American settlers would colonize nowadays a Mexican border state.
The EU has destroyed worker's rights in Western Europe, the economy in Southern Europe, and the labour force in Eastern Europe.
There are also lots of knock-on effects.
For example: in the last decade, the Netherlands has seen "homework institutes" popping up like mushrooms, which are more or less similar to Asian-style cram schools. At the same time, there's been a big push to lessen the impact of standardized test scores in favour of American-style 'holistic' admissions.
Why? The open labour market.
It used to be (and for the most part it still is) that at the end of elementary school, you took a test which decided whether you were going to the vocational track or the academic track in secondary school (though if you ended up doing unexpectedly well or badly, you could still be transferred afterwards). At the end of secondary school, everyone takes another countrywide standardized test, which determines a) whether you passed and get to graduate, and - at least in the academic track - b) admissions priority in case there's not enough room for all applicants. ('B' has been abolished by now in favour of 'holistic' admissions, however.)
Even 15 years ago - which was the year the Eastern Europeans were allowed into the Western labour markets, people generally didn't get too bothered about these tests. It generally ran in families anyway (which you'd expect). If you went into the vocational track, then there was nothing wrong. E.g., plumbers and electricians made decent money, and even the lowest ranking jobs still got you enough to afford a roof above your head, enough to eat for you and your family, and a yearly holiday on a Spanish beach - the fruits of 100 years of fighting for labour rights.
Then the Poles came in. After them, Romanians, Bulgarians, everyone. You can hire them via agencies in the home countries, so that Polish/Romanian/Bulgarian labour law applies. (This means that a Dutchman is legally prevented from competing even if he wanted to: Eastern Europeans are often paid well below the Dutch minimum wage, and it is illegal to pay a Dutchman such a wage.) But they come in by themselves as well. They even compete with teenagers for €2-3/hr jobs as farmhands. They competed the teenagers out. Then they competed everyone else out - largely due to being willing and able to disregard or circumvent labour laws. There are basically no more Dutch construction workers, for example, and fewer and fewer Dutch plumbers or electricians. Blue collar work is no longer available for Dutch people.
So how did people react? Everyone who stood a snowball's chance of succeeding at it went all-in on education. Thus the cram schools. Then, the traditional elite found out that their kids aren't really anything special when the whole country is suddenly doing its utmost - thus the admissions fuckery. And now here we are.
Even then, the people who just don't have the IQ for getting a fancy degree (easily 60-70% of the population) are screwed; and even the ones who do are increasingly finding out that there's no market for that many educated people. It is partially their own fault for picking the wrong field to study, but even then, STEM fields are even harder to do well and then there's the admissions fuckery. So now they're just left with a bunch of student debt - did I tell you the government abolished the basic student grant that all college students used to qualify for, when that became too expensive after everyone suddenly wanted one?
I'm sure the Bryan Caplan types only see upsides here. After all, the Poles are better off than ever (even if they're worse off than the Dutch would've been). The Dutch are more educated than ever. And GDP is up, isn't that great! The Excel sheet says that the world is better than ever before.
But if you look at it from the ground, the reality is this: everyone's more stressed than ever. Everyone's working ever harder and living ever worse for it. Except the people who've been relegated to welfare and uselessness, who just drink themselves into an early grave. But hey, GDP is up - yes, if you squeeze harder, more comes out, but that's no fun for the people being squeezed.