Depends on what do you mean "live better". iPads, cars, plane tickets, electronics and other luxuries aren't cheaper in Poland than they are in US. You might "live better", but you also might never be able to visit Hawaii or drive a Tesla.

By live better parent commenter almost certainly meant make more money.

Even if luxuries are not cheaper, food, shelter, healthcare etc. are, freeing up more monies.

Depends on your living situation. If you want a house in the suburbs with not terrible commute, it's going to cost you $200-400k in Warsaw vs probably three times as much in SV? This (and higher taxes in the US) can probably consume a lot of the salary difference. But, on the other hand, if you're ok with living in a small studio, you're going to make bank in SV.