I was wondering this myself. I fear that the separated design of the new notifications is by nature incompatible with sorting them by app. I'd love to be wrong on that, though!
Well, far from being completely useless, just perhaps not as useful to those who are used to having it grouped by apps (and/or perhaps sorted in a different fashion other than time).
I've been using iOS 10 ever since I wrote that comment, and I've since grown accustomed to the chronological grouping of notifications. I'd change it back if Apple ever offered the option, but I don't really care if the option comes back or not.