https://en.wikipedia.org/wiki/List_of_rotoscoped_works#Anima...
The experienced animator and inbetweeners knew how to produce smooth line motion, and the live action was used for lifelike pose, movement, etc. It wasn’t really tracing.
There’s examples of this in the Disney animation books, the finished animation looks very different from the live actors, but with the same movement.
Animation is a great art and it takes a lot of skill to make things look the way they ought to for whatever it is you are trying to achieve.
Most animators don't like the "digital makeup" comparison (because it's often used in a way which feels marginalizing to their work on mocap-heavy shows), but if you interpret it in the sense that makeup makes people look the way they are "supposed to" I think it's a good model for understanding why rotoscope and motion capture don't yet succeed without them.