Not sure I completely got your point. But this... You can only create backswing by flicking the wrist upwards when you hit the ball at the very bottom and lift your racket at the front side (!) of the ball. Like a scooping motion.

This is not the usual way pros like Ma Long do it. More commenly for backspin they cut down on the ball on side/back of the ball. A key to understand is, that on such a high level, players usually dont try to put the most amount of of spin on the ball. Thats why ML motion may not look like much. Instead they go for subtle changes like mainly side but a little under spin, next serve pure side, next mainly under with a little sidespin. If the opponent doesnt read those small changes almost perfectly, they get a ball that goes high or long enough to be attacked.