I think you are confusing CGI with post effects. You can have CGI "in camera" as they call it. The Mandalorian pioneered this. The system uses massive LED displ

I think you are confusing CGI with post effects. You can have CGI "in camera" as they call it. The Mandalorian pioneered this. The system uses massive LED displays and Unreal engine. They call it "The Volume". https://ascmag.com/articles/the-mandalorian https://ascmag.com/articles/the-mandalorian On the other hand you can do non-CGI effects in post as well. In fact its super common. Bluescreens, compositing, rotoscoping, etc were all common techniques well before computers had anything to do with film making and can all introduce the problems you describe. It was actually a common problem. People would spend a lot of time tryng to get lighting to match and to line up composited elements. So its not a CGI problem at all. Its an in-camera versus post effects problem.