A passive backstroke pull isn’t going to create much propulsion.
Swimmers have to pick up the hand speed to maintain pressure on the water and create propulsion.
If swimmers can focus on a patient setup and an aggressive finish, it usually gets the job done.
Using some sort of resistance can be really helpful because swimmers can FEEL the pressure building on their arm.
That reinforces an effective strategy and creates more awareness of what needs to happen.
Add stroke counts and speed to the mix and they’ll get objective feedback as well, continuing to reinforce effective skills.