When you have a gradient and you want that gradient removed you can allow the gradient to do some work while it excuses itself. When you have time/throughput constraints that you can only achieve with a fan then yes, adding something extra in between will likely fail making up for the additional fan power required. But in the same way as you could do away with the fan by increasing the size of the radiator involved, you could also tolerate a gradient harvester in between, by making the radiator even bigger. No physical principle broken. Economic principles broken? That's another story...