(not the parent, I don't have a specific number)

Generally speaking, the economy is not a zero sum game (by definition), or we would never have made it past the first 50 people in New Amsterdam. Every person here on a visa interacts with the economy (needs to buy groceries, etc). Presumably they create more wealth for the economy than they cost, or it would not be worth it for a company to hire them.

I think a more interesting question would be if, for the particular occupation (say software engineer), a person on an H1-B visa adds more than one jobs worth of demand for more software engineers. Even if they benefit the economy as a whole, it is still possible that a subset of the labor force sees extra competition. That opens up the question of is it better to suspend the program to protect a subgroup, or is it better to expand the economy as a whole.