What do they mean is this “best system”? It is the system, period, of the United States - the President of the United States is just that - the President of the UNITED STATES - and is elected by those STATES. That’s our system of government - individual entities that joined together to form this union. There is nothing official about a “national popular vote” - they are just tabulating together the results of completely separate elections that are not related to each other. These are individual separate local elections put in place by the individual state legislatures - they each individually decided to grant their citizens the right to choose the Electors of their individual states.
Thomas Jefferson originally referred to it as the united States of America, small u, in the Declaration of Independence. The new country was the 13 colonies that were declaring themselves to be States of America which were united. I love the way their minds worked.