> That assumes the demand and the supply are independent variables.
When the argument is that an increase in supply causes lower wages your counter argument doesn't make any sense at all. For wages to rise the demand has to grow faster than the oversupply. The primary way to increase demand is by lowering the price of a service aka workers get paid less.
In other words it is possible that even with an extreme amount of immigration everyone still gets a decently paying job but in the end wages across the market have fallen.
Whatever pie analogy you're trying to pull doesn't matter. I don't know why people keep getting nerdsniped by that word and often even use their own hyper specific definition of it which doesn't match the definition of the other person. There is no law that says people always benefit from a growing economy and there is no law that says people can never benefit from a shrinking economy.
More people would mean smaller pieces if the size of the pie held constant. But what if there are also fewer people making the pie?
In reality, it's even more complicated in that the contribution of the pie making is not proportional to the headcounts either.