Of course you should have soffit venting, but forced ventilation results in negative pressure, regardless of whether that venting is a cupola harnessing the wind or a motorized fan. That negative pressure will pull conditioned air out and building science research shows higher attic temperatures are better than forced ventilation.

Even better is larger amounts of passive ventilation, but if the only thing you change is adding forced ventilation, then you're creating negative pressure and this is worse if using A/C.

The cupola does that using the "stack effect" and the acceleration of the wind as it hits the sloping roof, at zero cost!

That said, I do have an attic fan connected to a thermostat. I'd rather have a cupola, though.