The framerate drop is due to them locking it to 30 fps. It was variable before so you would get smoother areas than others and thats why you would get screen tearing because the framerate was going out of sync with most TV's that run at 60Hz. The update has fixed this issue but the framerate is now at 30fps but occasionally the og PS4 can't keep up with the fast movements and you would get stuttering. Networking is also a factor that can cause stuttering and low frames.
As a experienced PC player and graphic settings tinkerer lol. I would say the update turned off ambient occlusion thats detailing on edges, lowered shadows to very low, lowered the lighting quality and of course locking the framerate to 30fps. This has definetly reduced the quality of the graphics on display but its now not stuttering as much. You can't have it both ways sadly.