But even under the best of circumstances, the dubbing crew and cast will be at a disadvantage compared to the original production. They have the awkward job of balancing mimicry of the original seiyuu, handling the translation, and conveying the original characters as well as possible.
There are plenty of good American VAs and plenty of good original American animated series/films with excellent voice acting, led by great directors. When it comes to dubbing, however, it's a very different matter.