So there is no link between immigration and employment levels?
because of regional factors, employment sectors, etc, things are not as simple as you want to make out.
The point is that the government will have a lot more control over how it wants to manage the country – if it wants to effectively carry on with high levels of immigration then it can, if it decides it only needs baristas for Costa and Starbucks, then it can also do that by only issueing appropriate visas, etc.
If it decides it wants to let capitilisaton and globalisation run riot and lay waste to areas of the country and the workers there, then it can.
If the people of the UK decide that they don’t like living in that sort of society, perhaps they want to move to a high taxation environment like Sweden, then they can vote out that government and install one that has the power to change things without being hampered by the EUs vision of how things should work.