It's not as if Poland and Hungary would have been booming economic superpowers if it hadn't been for the EU. The people fleeing their country because of the lack of jobs won't suddenly find new jobs if they can't leave.
The exploitation of cheap, foreign labour is an issue though and it's not just hurting the people being exploited; the natives of the country the exploitation takes place in will see their wages drop if some shady outsourcing company can have the same work done for half the price. Those old people don't want their assets wiped by someone who can barely understand their language either but they need to put up with it because of cost-saving measures that has degraded the level of care. This is something the EU can change, but the many labourers who'd be out of a job if the EU added more restrictions to foreign travel wouldn't agree with changing the policy to make them unemployed.
The double production line issue would just come back in a different fashion if quality goods weren't exported; there'd be no money to be made selling most of the goods, so they either become a luxury product or only the cheap, garbage production line remains.
Despite all the known problems, countries like Albania, Macedonia, Bosnia and Herzegovina, and Serbia are all applying for (or already negotiating) a position within the EU. If they would really be better off without the "dysfunctional" EU, they'd form their own bloc or remain independent. Even for poor countries, the EU brings benefits.
Case in point, the EU is already working to prevent/mitigate this : per 2021, local business must pay adequate local wages even to foreign workers.
do you know why they do this? They can see how easy it is to milk the EU for money in ways that benefit these mafia states. The major of Zagreb is connected to the Bosnian Mafia, he just spent some time in hospital (the mafia put him there but you won't read this in the news). The top lawyer of Zagreb is an asset for the mob. If you want to kill somebody here it's possible to make that happen for very little money. Have you been to Albania, or Macedonia? You should seriously go there before assuming that absorbing them in the EU is a good idea. I'm all for bringing in the people of these countries but before that can be done the organized crime there needs to be cleaned up. The result otherwise is that you'll enrich those that don't deserve it.
The TV series McMafia was set in Croatia (even the non-fiction book and the TV show plays out in a global theater). There are good reasons why that country was chosen for the series. You want to meet some dangerous people? I can introduce you to the guy who shot the Minister of Tourism here not so long ago - he is my age and now runs a drug ring in Austria. This is common knowledge here and as normally talked about as the weather.
Ah yes the guy who now runs Rimac (the super-car company that competes against Tesla) https://en.wikipedia.org/wiki/Rimac_Concept_One his father is also connected.
My GF's sister was recently alerted by the owner of the building that the mob has asked them to isse them with keys to their flat because they refused to sell it. The person refused to hand it over and alerted her. The poor girl now lives in fear every day.
The Balkan is the wild fucking west. I live in one of the most civilized parts of the region and love it here, because it's also easy to stay away from this all. If you think for one second that the state would want to ( or even could) protect you, you'd be wrong because they're all part of it. If you're rich you don't pay any fines, if you're poor you get fucked. It's always been this way and thanks to globalization it's getting worse (more ruthless competition from foreign mobs fighting over territory).
I can go on and on ... but Misha Glenny's "McMafia" really explains it all rather well.