You assume migration is like that scene in Dad's Army where the recruits are marched into the vicars office and Mainwaring is flattened against the back wall as more and more push their way in. The FoM we had in the EU was fluid -people came people went if you were a Polish builder and the market place was flooded you were free to try your hand in Belgium or Germany. The idea you could just undercut the existing building industry and keep undercutting it was bollocks. As a builder in those circumstances yeah you could cut your own wages but then how do you live here? Materials are not something you control. Jewsons didn't do special prices on roof timbers for Poles.
If there were Romanian dentists coming here then good we need them - it takes 7 years to train one and we have depleted the places at med schools to teach them but instead we make them unwelcome and they go elsewhere ( happened twice in the last 4 years at my local practise and there are now no NHS dentists in town)
As for "doing the shit jobs" - I have 2 observations about that.
1/ How dare you say somebody is doing a shit job - ie one thats not worthwhile - who is emptying the dog shit bins in your park? Who is cleaning places of work out of hours? Are they poos saps doing shit jobs because they deserve to?
2/ Brexit was about everyone getting trained up - getting better, well paid, high tech quality jobs we were told. That is not happening as funding is cut on training etc but you still expect the shelves stacked at your supermarket - it was nothing to do with benefiting the vast majority of that population but sadly for their own outcomes they fell for the lies.
See you at the foodbank later comrade.