If you grant independence to Puerto Rico, half the island will move to the mainland.
Half will go to the main land, the other half will sell the island to China, take the money and move to the mainland.
With independence, their residents would not have automatic U.S. citizenship or the automatic right to immigrate to the U.S. They would be like the residents of any other country in that regard.
That's fine. As long as they're not going to get 2 Senators.
5.9 million PRs live in the USA
3.2 million PRs live in PR.
so nearly 2/3rds of all PRs live in the USA already