There is a discrepancy between the piano-vocal score and the orchestra score. The orchestra score does not contain this indication for the chorus, and the legato with dots under it is for the woodwinds and lower strings. So, in this instance, we are reminded of the shortcomings of the publishing process. We always have to double-check the orchestra score and check other editions, if available, when questions arise.

I agree with you that Verdi did not intend for singers to sound unnatural. I also feel that, as with virtually all music from Mozart through the 1930s, the phrasing should be both dramatic (in accord with the text and situation) and naturally unaffected.

These indications for strings also appear in wind parts and they are not entirely natural there either. I have always found that (along with plain staccati or accents) this indication must be taken in context. I think such indications are somewhat figurative and meant to direct the singer to phrase in a certain manner that parallels—but does not necessarily duplicate—what would happen or is happening in the strings.

For example, consider Act I, three before 15, in Renato’s aria, Te perduto, ov’è la patria. I feel it means to increase the diction with the implication of moving to the word patria, which is slurred, just as six notes articulated in the same up-bow leads more decisively to the following down-bow.

For me, there is no such thing. There are national and regional styles and implications depending on the period. There are many similarities in the notation of Vivaldi, JS Bach, and Rameau, as there are in the notation of Puccini, Richard Strauss, and Debussy.