Wing Chun has been described by some as a simple system - simple does not necessarily mean easy but it does denote an element of simplicity.
People commonly recognise Wing Chun as being demoted or comprising three empty hand forms, the wooden man and the weapons. However, in my experience this is the skeleton of the "system" which encompasses so much more especially if one also includes Gulau Wing Chun as well as the more commonly recognised and represented Yip Man Wing Chun.
I had been involved in the study of Wing Chun for well Over a decade and had trained in Hong Kong with the sons of Yip Man before I was even aware of the breadth of information associated with Wing Chun.
For example Dai Lim Tao ( The big idea form )
Many do not even know of this form
Or it's existence, others dispute it and it's origins ( that lie with The famous Grand Master Leung Jaan ).
The easy answer to the this question is that the practice and study of Wing Chun is a lifetime process.
Depends on the teacher and style of wing chun. Some styles are as you said the bare bones and the head of the system doesn’t understand it. You could learn those in a couple of years and have nothing more to learn.