I know there is a difference between the "relative brightness" of binoculars with the same exit pupil and the "twilight factor" which comes into play when binoculars have different size objectives and I agree that a 10x42 and a 10x40 will be brighter in those conditions than an 8x32. This is something hunters should consider at that time of day. I don't know how much difference it makes under normal daylight conditions.
Oh yes, I agree. I was just making the pedantic point that the difference in light-gathering power between the 2 specifications was appreciably greater than the tiny difference in diameter might suggest.