I disagree with every single conclusion you come to in this.
First of all going back to renationalisation is something that'll never happen and also won't improve anything on its' own. You'd just see more conflict potential without a common European house.
The single European market is perhaps the worst thing to come out of the EU. It's what's destroying the poorer European countries currently as they cannot compete with the economic powerhouses that are Germany and France.
The reason Brexit happened is definitely not the influx of low-wage workers from Poland. This is completely absurd because that influx is the best thing that could happen to them. Why would you not want cheap workers who do the shittier jobs for you? If I were a hardcore nationalist and cared about my country the most I'd want lots of migrant workers from poorer European countries doing hard labor for low wages. The reason the Brexit happened was a mixture of fear-mongering, nationalism and people not realising that the neoliberal agenda of the EU will simply get replaced by a neoliberal agenda of the UK government. In the end not much will change for them since they will still be affected by the massive bureaucracy and all the regulations. Their currency is dropping like crazy though.
I generally agree that member states should have a right to self-determination but we need to overcome nationalism and racism in the EU and the working classes in all of Europe need to grow together and show some international solidarity. Only then can we actually improve Europe as a whole.