I’m 40mm boy and I have to say one must be able to continuously spin the ball hard to be consistent. Most of the reasons why it’s hard for me to practise that is NOT because of the ball but it’s difficult to find a blocker with a good touch. (People who touch so well tend to be quite a fair bit better than me so they seldom practise with me.)
Most of the time when I make a really really good top spin, my partners get panic and slap it with the wrist and hence I only have the option to power it up. (Obviously they can do that because they know exactly where the ball will land and they rush in, subsconciously fearing the spin. If the ball is just a little off, they mostly miss it) If I play with somebody who has a good touch, they know that if they slap the ball, they’re killing themselves because the opponent can smash it back quite easily. So they are very used to a soft block to return back all the spin, but not the power, forcing me to spin again. If I power the first ball without much spin. Then it’s the same, I’m killing myself because they can smash it back with ease.
People at high level seem to see this at the norm.
So spin has to go with a good touch. It’s the same for my training partner. The more I train him to touch better, the spinnier he naturally becomes.