and re: his last point about preference for european immigrants, i dont know whether that is true or not but the data you would need isn't just total population change over time, but some reference to the rate at which different groups are successful in legal immigration applications.
i.e. Maybe only 1000 europeans apply, but 50% are accepted, whereas 10,000 mexicans apply, but only 10% are accepted. you would still have more total mexican legal immigration even if a given european has a 5x greater chance of being succesful.
but even that would also be ignoring other explanatory factors like income, work history etc.