Ian Westermann, head pro at EssentialTennis.com, says although it may appear that the tennis greats rotate their racquets over the top of the ball when imparting spin, that's actually a myth, and the slo-mo video seems to corroborate his point. Of course, tennis and pickleball aren't the same, but some of the basics translate between the sports, and I think this stroke may also. While the strings of the racquet and the fuzz of a tennis ball will have more traction that a relatively smooth pickleball and smooth paddle, I feel his point may apply in pickleball as well.
Westermann's video and the comments below lead me to believe that the tennis pros brush up the back (right side) or top back of the ball, but they do not continue over the top with their stroke. Westermann's video shows that only those strokes where the ball is hit off-center end up with the racquet turning over: the physics of an off-center hit cause the racquet to turn.
As for returning shots with topspin: the best strategy is to wait longer to hit the ball. Having more time to assess where the ball will be gives you an edge that you lose if you hit the ball too soon. Topspin causes the ball to bounce lower than usual, so be prepared to get down under it and then lift up while hitting the ball. If you can wait until the ball is at the apex of its rise before hitting it, you'll have the best chance for a good return.