I'll chime in on the thermodynamics perspective, basically you're both right.
The thermostat opens at a specific temperature (usually it's a single temperature) which allows coolant to circulate to the radiator where it can release heat into the air moving through the radiator, so the engine temperature is regulated by the thermostat.
But here's the tricky part, if there isn't enough (or too much) heat rejection from the radiator, which can happen due to extreme ambient temperatures, clogged radiator due to internal calcification/external application of mud, or lack of air flow due to slow speed or broken fan blades the coolant loop can't reject enough heat to keep the engine in the desired operating zone.
This is why in very cold climates you often see big rig trucks put a blanket over their grill because the cold airflow through the grill at highway speeds never lets the engine reach proper operating temperature even with the thermostat stuck closed. The same basic principle (but in reverse) occurs at high ambient temperatures with low airflow (climbing mountains slowly in Arizona in August). Because your fan is driven by the engine belt it's linked to engine speed and goes no faster if the engine is too hot and furthermore because the thermostat is already wide open coolant can't flow any faster.
By reducing the pressure drop across the radiator you can get more airflow with the same fan speed, and the easiest way to reduce the pressure drop is give the air an easy way to escape from the engine bay - hence big holes in the hood. While technically "heat rises" due to density changes which cause convective currents, if the engine is hot the fan is on and convection contribution is small comparatively to the blasting fan. Alternatives could be a bigger fan (more required HP), a bigger radiator surface (aftermarket unit), higher coolant flow (bigger water pump), or something more exotic like a secondary cooler or intake water injection.
I like the cheap-n-cheerful improvement due to the hood vents, also, they look cool so that's a plus. I've been playing with the idea of installing a methanol/water injection system - but to be clear it's mostly for kicks and giggles and probably totally unnecessary...