There is a third option that we don’t want - go the way of Japan, ie no babies and no immigration. This would be the fastest way for the USA to not be a superpower. This is not going to happen.
A rapidly growing or rapidly shrinking population each have disadvantages. I’m just trying to understand the pitfalls of us still being around 330 million people 100 years from now with a generally stable births+immigration = deaths+emmigration.