Taking a random focal length, say 100mm, does a 100mm f/1.4 lens stopped down to f/5.6 let more light hit the sensor than a 100mm f/4 lens stopped down to f/5.6?
Now with a 100mm f/1.4 lens and a 50mm f/1.4 lens. Both set at f/4.0. They WILL have different aperture opening sizes. 100mm @f/4 would be 25mm. 50mm @ f/4.0 would be 12.5mm..