Either way you’re just getting airflow from the outside, so the cooling capacity is basically the same. The airflow patterns will be different inside the box of course, but either way you’re just exchanging air

We do this at NREL for plc enclosures installed outdoors specifically. We always have a fan on one side and a louver on the opposite (both with filters), so the airflow is basically the same whether your fan is pointed in or out.

I’ve always been taught to install enclosure fans blowing into the cabinet with the idea that you’re slightly pressurizing it and therefore dust isn’t being drawn into it through the seams. Genuinely curious what the reason you’ve heard for the opposite?