What someone's labor is worth is up to the market to decide. Also those $100k are taxed out of the employer and employee's value.
On the benefits of people moving to the US: it's been widely studied and it's basic economics, immigrants bring both supply and demand, so the size of the economy grows and so the opportunities to current residents.
Take the extreme: when people leave a country or city the economy there collapses, see Detroit or the increasingly old and depopulating European countries.
Or take the extreme on who comes: fiscal studies show that even low skilled immigrants are net positive fiscally. Only very old and unskilled immigrants are a fiscal burden.
Finally, thinking that we can capture the world's economy in a bottle and live lavishly without competition is delusional. If we stop letting people build here, they will build elsewhere and without us. We are increasingly less relevant.