i really like this thread, because i have spent many many years, 26 to be exact, doing both wing chun and grappling, so i see both sides of this. and here's my opinion on the subject...
BJJ Steve and Mook are both right. but if you haven't spent many many years doing both, it's hard to understand the other person's perspective. the difference in opinion comes from not understanding the other side of the "coin".
Wing Chun is about developing a "body structure", connecting it to your elbows, and using your forearms to constantly uproot and hit your opponent while your mind chases their center. Mook is right when he says, that if someone trys to armdrag you out of position, you are in actuality trying to drag a chunners entire "body structure" out of position. and if the body, mind, spirit are focused together, the armdrag actually pulls the chunner not sideways but right into your center. but as Mook knows, if the opponents "body structure" is better than yours, it is the chunner that will get pulled out of position. you also have to realize that in order to get this type of "effect" (being pulled into someones center), you must have someone use FORCE.
What chunners have to realize is that BJJ Steve is ALSO correct, because a grappler doesn't PULL your arm, in other words, he doesn't FORCE your arm out, he controls your elbow at the center with grips (think of it as a pak sau) and then PUNCHES you with his "body structure" (which is also straight spine). in other words, a grappler PUNCHES with their "body structures" exactly like a chunner connects their "body structure" to their elbows and release that energy out the hand.
in wing chun, we do chi sau which is wrist to wrist, forearm to forearm. in grappling, they do chi sau which is "body structure" to "body structure". but in essence it is exactly the same. it's just that chunners extend their structure into their elbows.
so a proper armdrag is EXACTLY like a pak sau and punch. except a grappler replaces the punch with their "body structure". this is why i always say that wing chunners are actually grapplers in disguise, but the goal of the chunner is to use the "body structure" into the elbows and shoot that energy out the forearm and out the fist to knock out their opponent, while a grappler uses their "body structure" to get into an opponent's body structure and take them down to submit them.
the goal is the same for both, which is to get the power generated from the "body structure", and without using "physical" force, get it to your opponent's centerline and/or center of balance and release it.
Jin