I can only speak for the WC Leung Jan passed to Lo Kwai. As others have noted circular techniques exist across a wide range of WC styles.
Sticky hand is not for fighting per se. The goal of Chi Sao for us is to learn to react to an opponents energy with out thinking. In other words to build reflexes, If I am pushed or grabbed or I intercepts an incoming punch you do not have time to think what is this attack and how do I respond. You just respond. Chi Sao is used to remove thinking from the equation.
You don't try to remain in arm contact. The goal of forward intent is to hit. If I am not obstructed I hit. Chi sao teaches how to clear a path to hit if your path is obstructed.
There are no blocks in wing chun. Chi sao will also teach you how to cover your exposed areas. part of that is learning movement how to move and where to move. One reason you move to the outside, side body, instead of up the middle is to use the opponents body to help block hooking movement from one side. The best way to stop a punch is not to be there. that is why footwork is so important. That is why people in the videos I posted to start the thread have so many problems. Non of them are using WC footwork. Triangle step,circle step, shifting step.sinking step etc and shifting are designed to help you change your angle and points of contact as well as change your head position.
Of course no matter what you do sometimes you get hit. Some one that spends time training their art be it boxing or what ever will get in their stuff. The key to getting hit is to be in a position where you don't absorb the full power of the strike which gets back to movement and position and covering or obstructing the open space.
This is our WC others may differ.