As Doug explained, things are a bit more complex. Light is gathered by the lens. Most film medium format lens are not very fast, so the camera does not gather more light than a smaller one.My reasoning is that a larger sensor gathers more light.
You could also see it in the following manner. For film cameras, the same "sensor" (the same film) was used in different sizes. The exposure of the film needed to be exactly the same or the film would be over- or underexposed. Therefore, per unit of surface, all cameras needed to gather the same amount or light (for a given film sensitivity).
Under these assumptions, a camera with film twice as large would "gather twice as much light". Is that what you meant?