Answer:) It depends which era you are referring to. We had immigrants arrive 22,000 years ago, 12,000 years ago, 500 years ago, and ever since.
The phrase American Dream was coined in the 1930s, so technically nobody came for the “American Dream” before then. But let’s look at the earliest European immigrants, Jamestown and Plimoth. They faced harsh weather, no experience with the local soil, only one big boat to travel in, nothing to fish with at the outset, and hostile indigenous tribes. Jamestown collapsed, Plimoth just barely made it.
Then you had three hundred years of forced immigration for Africans, and there’s no shadow of a doubt that their lives were the most difficult of all.
Italians, Irish, Poles, and other Catholic and Eastern Orthodox immigrants faced harsh discrimination. Clubfoot was one of the most common childhood maladies in Boston, because of walking in winter with no shoes.
The Chinese were invited over to build the railroads, then forcibly ejected, with serious restrictions place on Asian immigrants every few decades, and of course our concentration camps for the Japanese in WW2.
Mexicans have always lived in the part of Mexico we stole from them, but the ability to cross the artificial border has been frequently adjusted, based on the political winds and the need for labor.
The one thing that makes life a bit easier now (along with general societal progress in hygiene and healthcare, etc.), is that many cultures and ethnicities have support networks in most major cities. If you are a Korean family who just arrived in Brooklyn or San Diego, there will be other Koreans willing to help you find work and housing and healthcare, etc. Plus, of course the Internet and tools such as PayPal, where you can stay in touch with your family and repatriate your earnings much more easily.
But unless you’re a Saudi prince or the child of a tycoon, an immigrant’s life is always difficult.