The idea of a basic level of income isn't that it goes away once I find a job that pays the same or more, it's that I'm always guaranteed that base pay. If I take a job that pays an additional 2800 per month, then I'm grossing 5600/mo.

I don't think there's any reason to believe that low paying jobs will just go away, and more reason to think that the people who want nothing more than those low paying jobs will take them.