Metric is no more accurate than US customary units.
No, the issue is that the use of it is much more accurate, as expressed above, the americans have a deer love of using the wrong units even within their own system.
They use volume units for compressible things
They use volume units for undeformable things
They use volume units for things with large air gaps between them and inconsistent shapes
They use the same words for volume and mass units (oz in the US can interchangeably mean ounces or fluid ounces for example)
In general, trying to follow a US recipe that needs some level of accuracy is basically impossible. If you're trying to bake bread, you'd better have a metric recipe, or you're screwed.