Everyone pays taxes so I’m not sure why uncle Sam’s cut matters; it’s going to be nearly the same as working in a regular job.
As per your math, you added them together… percentages like that are multiplicative since you wouldn’t get taxed on the fees paid to steam, so it’s really more like $227.50 in your example. Still less than half, but all your additional fees or whatever get deducted out of the big 35% bucket.