I think of translations as passing some scholarly smell test: you can read the words of the translation and be reasonably sure of what the words are in the original.
I can't think offhand of any American poets who have Mandelstam's urgency, but it's a different country and a different time, and I don't think it would make much sense to say that this is something that's "missing" from contemporary American poetry.
I don't think that someone who does not speak the original language can ever expect to produce a real translation.