Class is profoundly salient in the United States. Unless you've been on the outside it's very difficult to see, because the gradations are more subtle, but they run no less deep.
Of course class exists in the US, but if you're able to move up in a tax bracket people won't judge you for having come from a lower tax bracket.
Rubbing elbows with rich investors and CEOs from affluent backgrounds is definitely more difficult for someone from a lower class background.
With maths, you can work as a professor or work in finance. Two domains with limited demands that are highly competitive.