taking something that is cheaper to keep costs low has always been the case. see slaves, see why emperors and kings conquered other worlds - for resources and cheap/free labour.
The way we pay people today is nothing but that. just modern slavery
we depend for our cheap coffee to cheap coders on other places where we didn't have to invest our time and money to get them over quick and get them working (bringing us money)
I came to London some years ago when Romania still needed working permits. it took 6 months to get one and the company had to sponsor me. it was such a pain in the arse even for a multinational with 60.000 employees that they said they will never do it again. we now are looking at exactly that.
yes, there will be more opportunities for poorer performers to earn more money purely because of process of hiring, but that money will be worth less than your salary is today because of inflation, import taxes, etc
You have to be really daft to believe a hard Brexit will bring anything good.
I hope I am wrong