Does the concept of Capitalism increase the net wealth?
Here is a graph of labor productivity per hour for the United States since WWII.

This is fairly typical of capitalist economies. Even Karl Marx and revolutionary socialists recognize that increasing labor productivity is a general characteristic of capitalism. So yes, the pie keeps getting bigger and bigger as a result of this in combination with population growth.
The question of inequality is a somewhat separate one. If the whole pie is growing big enough, the absolute size of my slice can grown even if my relative share as a percentage of the whole is getting smaller. In other words, the total wealth of society keeps increasing, and so in absolute terms, even the poorest see some benefit. In relative terms, that gets more complicated.