Yes, the U.S. can continue to dominate the world economy without improving leave policies. One of the reasons the U.S. is so historically strong economically is because of the current leave policies. Paying someone for a year for work they're not doing does not strengthen the economy, it weakens it.
I believe this is a key contributing factor to why the U.S. economy is the most dominant. The maternity leave and vacation policies of companies in this country pale in comparison to other global powers. Fifty and sixty hour work weeks are not uncommon and our obsession with careers, regardless of how they affect our health and personal life, shortens our lifespan. We avoid taking vacation time for fear we will be replaced by someone who doesn't. This is what drives our economy and the only ones who benefit from this are the companies and the economy we work for.
A small business cannot possibly just pay two salaries for an entire year because the government dictates. Most employers have a hard enough time hiring people to work for them as it is. Employers will be afraid to hire women and they will be afraid to pay a living wage. This is a losing situation for the United States.
Serbia has a population of slightly more than 7 million. The United States has a population of well over 300 million. The two economies are very different and it is much more feasible to cover the maternity leave with a population of less than 8 million. The economy of the United States is already much stronger than Serbia's.