Spanish dubs of animé are sometimes good. All English dubs I've heard are atrocious. I remember one of the first dubs that was lauded was the English dub of Princess Mononoke... and it's hilariously bad, even if it has big names doing the voices. The Japanese version is the best, but even the Spanish dub is better.
A dub is like a cover, agreed. Almost always, a terrible cover. I can always tell when I incorrectly set the language on Netflix to something other than the original -- you can immediately tell it's a dub because of the drop in voice acting quality. English dubs are particularly terrible, it's like the voice actors are emotionless drones, and when they try emotion, they use it in all the wrong places.
Besides, it's disrespectful. An actor/actress is not just their face and mannerisms. It's their voices, too. The voices are an essential part of their acting (if you are deaf, you can't help missing them, but if you are not, unless it's a scene without speech, you're missing a key ingredient). Saying "ok, I'll replace his voice with this other voice, and his face with with this other face I like better.. you know what? I'll just edit him out of the movie and replace him with this other actor I like better!" is way too scifi and post-cyberpunk dystopia for me. It's just disrespectful.
I cannot honestly say I watched a movie if I watched it dubbed. I watched a cover instead.
What you're saying is effectively "our voice actors are better than the original actors", which I simply cannot stand behind.