"Bensi: cong. ma piuttosto, ma invece, ma anzi (con valore avversativo DOPO UNA FRASE NEGATIVA; anche preceduto da ma rafforzativo): non mi pare sciocco, bensì svogliato; non hai ragione tu, bensì lui; non fui io, ma bensì lui che lo offese | ( non com.) tuttavia, però, peraltro (con valore limitativo): gli dissi di no, bensì a malincuore "
Sorry, I am not a native speaker. I have found these 4-5 examples. As you can see the first sentence is always a negative one (una frase negativa) and the word "bensi" is used only after a negative sentence with the meaning "but". Non hai raggione tu= you are not right, bensi lui= (but) he (is right). Bensi=ma , but it cannot be used generally. Take it easy, we do not have to know all of the rules to be able to speak a language.
Bensì is something that we don't really have a consistent translation for in English, but I always use "but rather". But it essentially follows a "Not a but rather b" pattern. A parallel but does exist in other languages. It is sino in Spanish, bensì in Italien and sondern in German. I would assume it also exists in languages that I don't speak as well
Well you included the wrong subject pronoun for the meaning of the sentence, (it's talking about what "you" are not what "I" am), but I think just adding any subject pronoun where none exists in Italian was sufficient to make that a poor translation. To the extent parallel modes of expression are available, they are the best translations.