It's basic economics that more workers with fewer rights lower wages across the board. "They make what Americans do" when there is a continuous flow of competing labor. Sure. What would companies pay if they didn't have these exploitable workers? Would the companies have opened new office closer to where Americans are educated? Certainly, one of those two would happen.

But it does negate the claim that H-1Bs are paid the same wage.

If your claim only applies to a subset of visa workers in a subset of companies, then refine the claim to use a word like "some", and it will be a trivial claim that I agree with.