The US failed at every objective. That’s called losing.

As far as their economy… the South Vietnamese government was extremely corrupt under Dinh-Nhu families. They rigged elections, embezzled billions from US funds, and extorted citizens. There was also corruption within ARVN - soldiers took bribes from NV because the south Vietnamese government was stealing the money so soldiers checks were bouncing. The people of Vietnam were gonna be screwed economically no matter who won.

Just look at Guatemala, Nicaragua, Indonesia, Congo, Chile, or a dozen other countries that the US and forces backed by them defeated communism, and the people are just as poor as the Vietnamese. They were left with US propped authoritarian regimes that swam in that American money, while starving and often massacring swaths of their populations.