Attuning definitely does not work.
7 guns now and not one are what I attuned.
So attuning doesn’t work or is so marginal as to be irrelevant.
-
My anecdotal evidence suggests that I have been getting more drops of the weapon I have attuned, but as ever, nobody knows what the concrete figures are. I think we expected it to be 100% target farming, so the fact that it isn't throws a lot of questions up.