Peabody writes:

Why is a suction-side cleaner worse than a pressure cleaner?

Because there is virtually no power there to do mechanical work.

The pressure-side power makes the cleaner scoot around like a rabbit,
covering the pool much faster. Meanwhile, the venturi effect makes it
circulate enormous volumes of water through the bag.

Being thus more effective, the cost is lower, because you run it on a timer
for short periods, not all the time, and the power cost is ultimately the
dominant true cost, not the purchase price.