You're correct, mass immigration from around the world will not be halted merely by Brexit but, a hard Brexit is a step that we have to take, if we're to ever rid ourselves of the cultural marxism that has infested Parliament, our Civil Service and our Education system.
The United Nations Migration Pact, fully endorsed by the EU Commision, is on the table for treacherous Western Governments to sigh up too.
There's numerous videos about it but they're being taken down by the leftist Silicon Valley indoctrinators, as quickly as they're being posted...
I suggest people stop yapping 99% about the economy and look at a more pressing issue.