For my standpoint, I do think JBJ will, eventually, hit major league pitching. My position is, he's already had more time to figure it out on the job than Pedey needed. He'll get it eventually, but maybe not necessarily on our timetable, more like Lowrie. So it might be a great idea to have someone around who can cover for the kid in case the adjustment period takes longer than we hope it does.
I'm fixated on Blanco as a solution for 2 reasons. First, he's likely to be available. The Giants are looking to do some shuffling in the outfield and I can't imagine them being particularly averse to dealing him for a fair price. Second, Blanco is in truth what we actually need backing up our rookie -- a guy who can get it done himself, but won't outshine the rookie when said rookie starts to produce.
If JBJ doesn't produce, which I don't believe is the case, Blanco is a very good bottom of the order roster filler type who won't hurt you as a starting CF. He's not great, he's not an all star, but he is useful. If JBJ does produce, Blanco is the stuff championship benches are made of. I expect the team to be hoping to bring in, maybe not Blanco himself, but a player in that mold (~2 WAR 3 position OF who stacks his production towards OBP) if the deal is there and the price is right, because it's a move that would make our outfield more resilient than it is right now.