https://georank.org/assets/img/charts/economy/poland/slovaki...
Meh, idk what magic maths they pull, but any other sources I find do not corroborate their graph.
https://www.researchgate.net/publication/352708343/figure/fi...
https://dimiter.eu/Visualizations_files/cee/gdppc_country.pn...
Slovakia and Hungary have trailed % growth compared to Poland, but they are far richer countries now that they were 20 years ago, and the GDP per capita for Poland, Hungary, and Slovakia is quite close to each other[0].
I'm not trying to say Poland didn't do well, it did! I'm just saying the advantages of being in the EU outweigh any national merit by a lot, which should be quite self evident.
[0] GDP, nominal, per capita: 31,336 / 28,430 / 31,242 https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nomi...
Ukraine saw similar rise of PPP per capita as Slovakia and Slovakia wasn't even invaded in 2014.
Switzerland's GDP per capita PPP growth is same as Slovakia and Switzerland is not in EU.