If you really want to get into the details, I recommend the book “The Economics of Immigration” by Ben Powell.
It talks about the distribution of the kinds of people who seek to immigrate and how they tend to compliment the local population.
For example, immigrants tend to be either high skilled (college grad from Mumbai) or low skilled (border crosser looking for work). Those sub-populations are both lacking in the mainly middle-of-the-distribution American populace.
In addition, people tend to immigrate when they’re in the prime of life. Young ambitions adults who want to work and improve their lot. They’re already through childhood and not yet near old age—the two times of life when people tend to consume more resources than they contribute.
Everyone tends to be better off with more immigration.