I bolded the part where I believe you are mistaken. A middle aged person will have a maximum pupil size of 5mm, a young person will have a maximum pupil size of 7mm. Elderly is about 4mm. During the day, everyone's pupil is about 2-3mm.
Everything else you've said is true for a young person. But you've presented a larger objective as an across-the-board benefit for anyone in low light, which I don't agree with.
The only gain for a middle aged person is during low light when the scope is between 8x and 9x, and even then it's only about a 10% increase. (as you mentioned vignetting, when you're in a position to take advantage of the edges of the exit pupil, you aren't adding a light improvement that's linear to the added size because the edges are dimmer.)
I disagree with and/or.
If you have large pupil, AND hunt during low-light conditions, AND you're using your scope between 8x and 9x, you'll get a small improvement in brightness.
And are all these 3-9 scopes?
If they have near-unlimited budget, and you're already lugging around a Barrett, "hunt" in total darkness, are generally younger than middle age, and always have great eyesight, and have a night vision system, I'm sure they can occasionally find some benefit in the extra size.
As far as I know, the Mil/LE long-range scopes most commonly used that have max-mag exit pupils similar or smaller than 4.5mm. So, for the most part, they frequently don't think the small improvement is worth the extra size and weight and mounting difficulties either.
I don't mind a discussion, but you're on the verge of degenerating this into a nit-pick. Like it or not, it is canon in the optics community that larger objectives provide the benefit of larger exit pupils, which can result in improved low-light performance and ease of viewing.
Your numbers on pupil dilation are a bit off. Maximum measured pupil dilation up to age 25 is around 9mm. Average at age 30 is 7mm. Average at age 50 is 5mm. People vary and the gradual constriction of the pupil is not a constant, but those are generally accepted numbers from my sources.
With respect to an "across the board benefit", I was quite specific actually and attention to the example clearly demonstrates that there is a cross-over point in the magnification spectrum where a large objective does or does not offer any benefit.
Read: I stated from 7x on with a 3-9 scope and the numerics were pretty specific in terms of pupil size in relation to exit pupil size. Apologies, I should have spelled it out.
The cross-over point or sweet spot (in terms of brightness gain) is the area where the exit pupil of the larger objective is greater than that of the exit pupil of the smaller objective, and the exit pupil of the smaller objective is less than the actual pupil diameter.
The benefit is not "only for young people", but rather for those with pupils that can benefit from the increase in exit pupil that a larger objective will provide. Likewise, you cannot marginalize the gain for "middle-aged" people.
You are also muddling my mentioning of the benefit of a decrease in vignetting with the benefit of a gain in brightness. They are separate benefits and at higher magnifications can be mutually exclusive.
With respect to your rehash of my statement:
"If you have large pupil, AND hunt during low-light conditions, AND you're using your scope between 8x and 9x, you'll get a small improvement in brightness."
You are not entirely correct in assessing a "small improvement". It may be a small improvement, depending upon the respective pupil. For some the gain will be very significant, for others not so much. If you are trying to establish that only "younger" people can benefit from larger objectives, there is some truth to that...but unfortunately that applies to most things that are fun to play with including pogo-sticks, cell-phones, sports cars and condoms.
The discussion involved 3-9 scopes, so I presented some numbers based on that. Regardless of the mag range, there will be a cross-over point where the larger objective will provide a larger exit pupil that can be of benefit, and also a point of diminishing returns.
"As far as I know, the Mil/LE long-range scopes most commonly used that have max-mag exit pupils similar or smaller than 4.5mm. So, for the most part, they frequently don't think the small improvement is worth the extra size and weight and mounting difficulties either."
The trend is definitely on larger objectives. Most "sniper" rigs have at least a 50mm objective scope, and very often a 56mm. The Hensoldt and Zeiss 72mm are not uncommon and US Optics has an 80mm that sees professional use. Why aren't they sporting 40mm?
You have an opinion that the benefit of larger objectives is not meaningful. There are configurations where your opinion is valid. Likewise, there are configurations where it is not. I'm not ashamed to say that the assertions I've laid out for you are not my own, but feel free to disagree with them all the same.