The lock screen idea, or ‘Cover Sheet’, makes the most sense in the context of iPhone X. You open the device by swiping away the lock screen, so it makes sense that you should be able to pull it back down. The lock screen behaves like an extra layer on top of the system UI.
This design feels a bit odd on other iPhones, especially considering how quickly the lock screen flies away when you unlock with Touch ID. You can barely see it as it rockets off to the top!
I think the idea of replacing Notication Centre with the lock screen is cool (especially with the gesture interface), but they made it too simplistic in iOS 11. I’m happy to see that it’s evolving nicely in iOS 12. Apple does listen to feedback, it’s just a bit frustrating how it often takes a year for them to make real improvements.