The Romans didn’t need worry about diluting their culture. They freely integrated foreign myths into their pantheon as a way of assimilating foreigners. They believed their culture was strong, too, not just their economy. That it could survive anything.
I think immigration is key to success to a country and controlling immigrations helps define the country.
That said, I thing you put up a solid thesis as to why open immigration is showing the strength of your country.
The Romans didn’t need worry about diluting their culture. They freely integrated foreign myths into their pantheon as a way of assimilating foreigners. They believed their culture was strong, too, not just their economy. That it could survive anything.