Do you have a citation for that? Wikipedia disagrees on the history (it's originally Italian before French: "Il meglio è l'inimico del bene"), and playing with Google Translate shows its ambiguious without context
Unfortunately, I don't speak Italian, but I feel a better translation for "the best" in French is "le meilleur". In fact, if you just click the swapping icon in the Google translation link you posted above, you'll see it uses "meilleur". "c'est mieux" = "it's better", "c'est mieux que..." = "it's better than..."
http://go/wiki/Perfect_is_the_enemy_of_good
https://www.google.com/search?q=le+mieux+translation