As I end up stating every time someone else believes they have the best ideas in the world, I am indeed a manufacturing professional, with a degree in manufacturing, and worked for the past 17 years in various manufacturing industries.
Now, credentials aside, I made no mentioned whatsoever of automation. An assembly line only refers to the process by which a product reaches one stage of a process, regardless of the number of stages involves. As it doesn't sound like you've ever seen other GMK sets because, all 'kits' like the pictures you have linked are produced in the same way, not on the same assembly line. Every ISO International, novelties, etc kit of keys is sorted and packaged separately from any other existing kit. So once again, splitting or adding is completely irrelevant, as you would be adding yet another assembly line in the process. In the very pictures you linked, that is one kit, and only one kit; the base kit as sold in every GMK group buy.
If you're trying to argue that your math makes sense from a capacity planning standpoint, you might have a point somewhere! Only to be diminished by the fact that you probably don't know how to calculate for capacity planning without a lot of additional information. Although it would still falter under the basic assumption of how they package additional kits in the first place: even if you reduced the number of keys in a particular kit, you're still doubling the packaging and assembly lines.
I see you like Dasher/Dancer as an example, and it's a fine example, except that you are referencing an entirely different and much longer process (8-12 months) from a company that charges a lot more. It has been quite a while since any Signature Plastics SA group buys had 'base kits', but those that did were easily double the cost with fewer keys. Thus, little loss was incurred in splitting what few kits were originally grouped together. Their kitting process is also far simpler (bagged and tagged).
At the end of the day, I will simply smile and nod at your passive insults, as I really can't fault people who don't know any better. When it comes to group buys for keycap sets, you will always have more than you need, regardless of what you buy, and there is nothing bad about it. In fact it is pretty important as most people have changing tastes for fancy or uncommon keyboard layouts that maybe they didn't originally plan for, but they may have keys for. As I've had to point out before, if you don't like having extra keycaps, throw them away if you are so confident! Or maybe just give them away to that guy who posted that would happily take anyones' keys who hate having extras.