As is your response, as it appears that you haven't tried my solution to validate it and then come back here with empiracal evidence with everything i provided even in RAW code format to try, im here if anybody would like to step in to offer advice, as well as just pinging me on a DF Discord site or ill consider just dropping my entire DF folder or mods for you in DFFD given that its virtually ready to release as is.
I take your meat exports with a extreme grain of salt as while things are handled in quantities the trade networks aren't that expansive* and are mostly locally centralised for worldgeneration activities, traders do not make rounds distributing to civ's currently in fortress mode as i know of and if the towers were being over fed, the solution is still the same by taking the meat out of Trolls to nip the exploit in the bud.
(for one goblins do not have trading animals, though dark fortresses are connected abstractly to pits and two, goblin civs do not interact with each other normally in any way i've seen so ill assume you meant sites)
Because reducing the amount of troll meat modifies the economy of the world in general, it may well have a knock-on effect that loops back to ultimately effect goblin (and troll) numbers. You are not isolating your variables (because you can't), which means that while you may be able to demonstrate a correlation between two things, you won't prove your hypothesis in the slightest. What you are doing is almost a textbook example of how empiricism and rationality are not the same thing.
Remember that the economy functions during world-gen, it only only gets 'frozen', along with the maximum population numbers for each site when the world is finished. Here is the thing, trolls count as livestock which means that all those goblin sites are producing a great deal of troll meat. Since goblins however don't eat anything, 100% of that troll meat is exported which means the total amount of troll meat being exported is *not* going to be negligible as you say. All major sites trade with each-other regardless of politics, that is a basic fact you can find out by asking people in adventure mode.
Goblin populations will always rise to 10000/250 per site. But the other civilizations numbers are constrained by food supply to be less than that. The means that if the goblins dump troll meat onto the markets of the other civilizations, then the numbers of those civilizations goes up. If the other civilizations are stronger, then the goblins will be less inclined to go to war with them but they are not so much stronger as to be inclined to go to war with the goblins. Since war is the only thing preventing both goblin and troll numbers from reaching their max, we can now see how reducing food output per troll can ultimately mean fewer goblins and trolls, even though neither eat anything.
This kind of behaviour is exhibited by trolls all the time as simple livestock doing out of place civilian things like claiming rooms and telling stories in the tavern (contrasted to a lack of voice oddly enough) and is a issue amongst people using semi-sapients tied to the fortress in fortress mode and on observation the many trolls with professions in adventurer mode. Besides this i dont see how adding non-sentients to be citizens would even be expected to turn out well, because semi-sapients have crossed the threshold needed but simply aren't full like the game expects and wants.
There are no semi-sapients in the game. The game works on the stark binary of livestockVScitizen, non-sapient VS sapient. When the game is offloaded, such as in world-gen it works on the former basis but when the game is onloaded it works on the latter basis, this creates silly situations I agree and was a very poor design decision on the part of the devs.
Trolls have professions because they have the
[CAN_LEARN] token, which controls learning work skills; that is entirely intentional. However if you have either [CAN_LEARN] or [CAN_SPEAK] (or both) then the game uses a special sentient AI which is not otherwise used, but only when the game is onloaded.
Im not giving up as much as becoming very tired with your flat rebuttals of whatever i say but as the point of the thread just try it for yourself and notice the curbed difference with a little bit of open mindedness. Or we could do it the other way and just mod in more creatures to disperse the numbers under goblin control with [ANIMAL] tags if that's what you're driving towards.
It is really not easy to dealing with a whole thread built entirely on false premises and misunderstandings. Goblins don't eat anything = FACT, Trolls as livestock don't eat anything = FACT. Given you made a whole thread premised upon the opposite of basic facts about the game, I don't see how the response can be anything but flat rebuttals.
Well there you go, that's a civilian population breeding anyway out of control, but a side-point of the suggestion thread is to always be aware that whether they are using the models or not, the food networks will always be active and influencial, though you would have to check some other numbers besides like approximate children to eternally lived spouse couples and child maturation. (the new divorces might break thing up a bit more to stop eternal spouses having two pages of children)
Overladen sites can pose to be a problem, so here's how you fix it in that food was pointed to be the issue in the OP and summarily control over it to be the solution or least a self limiter.
Food networks have no direct effect on the numbers of a creature that eats nothing. It makes a *big* downwards difference to goblin numbers if you make them have to eat, trust me on that because I have done it. I have a dark pits creature that doesn't eat and neither does it have a food supply, confirming that food supply is truly irrelevant to vanilla goblin numbers.
The civilian population is not 'breeding out of control'. The population always breeds up to a given number, that number is normally set based upon world-gen food supply but is also capped to 10,000/250 in the case of dark pits regardless of food supply. There is a hard cap based upon type of site and a soft cap based upon the food supply, for creatures that don't eat only the former applies.
The population will rise to the cap UNLESS something specific reduces the number below that. Typically that means war and presently war is good at killing lots of people off even on the winning side.