About the bold part, CT doesnt work instantaneously. It's just that Sasuke didnt make that black orb. When Pain used it, it was the first time of it being shown so it had to be a little bit special and unique. Now that it's already been used, he can just show CT regularly wihtout putting any emphasis on it. It isnt a huge difference actually.
What if CT works by the user putting up a field of gravity manipulation around the target?
What I mean is, when madara used CT he created a sphere of gravity that is manipulated thus attracting the rocks to the gravity point. What if every rinnegan user can do that and really all sasuke did was take that technique to a new level? Instead of creating a sphere of gravity (like nagato and madara), sasuke created a sphere of gravity around a living object and that's what turned the bijuu into the cores of CT.
If so, then couldn't sasuke do the same thing by creating a sphere of gravity around naruto thus making naruto the core to CT?
Weaknesses (every jutsu has one)
Itachi stated that the core of CT was it's weakness. So, it stands to reason that even if sasuke is advancing CT by making gravity cores around individuals, shouldn't naruto be able to defeat and break that core similiar to how itachi and bee broke the core of nagato's CT?
Idk. Kishi made CT very complicated by having sasuke perform it without an actual core.