I think translation inherently loses something? Just because the only way to render the poem exactly as the poet intended is in the language and cultural context the poet originally wrote in?

Not so much when the translator is the poet—there's a lot in Gloria Anzaldúa's Borderlands / La Frontera that she translated from Spanish to English (or possibly vice versa) herself. While I haven't read any of those poems with quite the attention to detail kaberett gives Neruda and Bly above, I don't think anything significant is lost in translation there. But usually the translator is not the poet, just ("just") someone trained in both languages, and (hopefully, when translating poems) also in poetry in both languages.

And I get the impression that translation is an art form in itself, but that itself is doubtless why kaberett is complaining that it's done poorly!