In both countries the governments are trying to make it quite hard to have people with Umowa o dzielo, which are de-facto employees, but do not pay the appropriate taxes nor are corrrectly protected. The employers also have some reason to do this, the protections offered to the employees often make it a very big risk to hire somebody. Regardless, i believe the southern European countries got it much worse on that front. (Note, the Polish social security model was heavily influenced by the spanish one).
What you describe is used by firms that you can smell a mile away and don't even try to work there.
I'm sure western Europe has similar companies that abuse employer rights.
Also, note that this is not an abuse of employer's rights: that's precisely how "umowa o dzieło" is supposed to work. That's one example of prevalent neoliberalism.
Yes, that's not a good proof, but you also did not present any sources.
As for neoliberalism: in Poland the usual way of employment, called "umowa o dzieło", gives the employee pretty much no rights whatsoever. It's almost as bad as in the US in that matter, and not comparable at all to Western Europe.