"The objective diameter has nothing to do with the exit pupil size."
Hmm?? In that case why can't I buy a pair of 120mm binoculars with an exit pupil of only 5mm and a nice widefield low magnifying power of, say, 6X? Those would certainly be a gas to use for all kinds of applications! But as I learned when I first got interested in optics as a kid of 12 or so, such binoculars, with optical systems capable of actually "concentrating" their light cones cannot be built. For ANY optical system, one can only lower the magnification at the expense of increasing the diameter of the exit pupil. Thus the binocular system just described, which has very large 120mm objectives, could only render a power as low as 6x with an exit pupil of 20mm -- since 120/6=20. This is simply an optical limitation we must all live with. Thus, despite what you may have heard or read elsewhere; "The objective diameter has EVERYTHING to do with the exit pupil size."
"The whole point is field of view - not brightness, which is a very slight bonus."
Well, yes, we certainly all love an ultra-wide virtual field of view, and one can purchase -- generally very expensive binoculars that have apparent fields of up to around 80+ degrees. Such binoculars will also provide significantly more"brightness," i.e. total light throughput, than a regular non-wide field glass of the same magnification. In fact, low power ultra wide field binoculars, with exit pupils up to around 7mm gain their amazing characteristics by being able to take any small region of the view and render it as bright as is physically possible.
This is why, mutatis mutandis, a 14x50 binocular, although it may have up to 2x the resolving power of a much more common 7x50 binocular, can, by the laws of optical Physics, never be more than 1/4 as bright per region viewed as the latter. Should one then step up to a 28x50 binocular, the resolving power could almost double again -- although in practice 1.5X is closer to the mark -- but the brightness would drop to 1/4 of the 14x50, and a mere 1/16th of the original 7x50s! 10x50 and 12x50 binoculars thus still make good sense to mass produce, since they have exit pupils of only 5mm -- for us now visually-challenged old farts -- or ~4.14mm respectively.
The aforementioned 14x50s, with exit pupils of only 3.57mm could, and do, also perform very well with higher resolution images still bright enough to satisfy for most purposes. That binocular size is, however, considerably rarer than the 12x50s, 10x50s or 7x50s. That probably has more to do, I would assume, with the simple fact that 14x binocs, with whatever diameter their objectives may be, are invariably quite difficult for most people to hold steady enough with their hands alone to be profitably used.
If one has ever viewed through a cheapo "ultra wide field" designated binocular, one will generally notice immediately that the image is considerably dimmer, and far less satisfying to view, than it is through any reasonably well-built binocular of similar power. Thus "brightness" is not "a slight bonus," but an absolutely essential component of any superior binocular.