Ok i relaxed a bit, my first few answers were mainly just impulsive, so don't consider them.
Sanala(11K P) has the same strategic location and the same number of towns as Jaculan (4k P) (they are far away from any war effects) the only difference is, one relies on oil and wine from close trades and inner consumption the other does not have these resources nor workshops either in them or nearby.
Starting from this one:
1) Sanala doesn't have the same stratigic location as Sargot. it's much further away from being sieged, and possibly the most well protected town in the game thanks to it's positioning.
2)Sargot has only 1 village that produces food, Sanala has 4, not to mention import from caravans. villages without food as a primary resources sell a tiny amount of grain sometimes, but not great numbers. this doesn't allow Sanala to ever starve or be short on supplies, unless sieged but that's nearly impossibile due to it's location.
2.1) Sargot villages are more raidable than Sanala's, once again thanks to map positioning.
3) the oil press has very little to do with this in all fairness. the town you should campare sargot to should be Quyaz, but even that one is not a good example.
4) Other towns with 4 bounded villages are usually high, on prosperity, thanks to constant food supplies. Marunath for example has 4 villages and 2 of them are dedicated to food production resulting in the town having good prosperity on average.
5) Seonen also has 4 bounded villages and even if none of them are mainly dedicated to food just the amount of villages is enough to make the town prosperous.
You are doing the same mistake they are doing, run a simulation and look at the end result. There is a lot of time the player has to live through in between and it can be quite off-putting to just shrug and say : "This will get better in 5 years" if ever that is.
This is Sargot since i started this run it has been starving, it is been a year without a war and this is how it still looks :
i played since january last year pretty much every day on every patch, i don't think i am making many mistakes when evaluating a good simulation.
I have run many tests, some of which have been tweaked for hours to find a good way to represent a standard gemeplay in a controlled setting, and if they don't i usually state that somewhere.
i also beat this game many times with limitations that many players would find hard to say the least, and that requires a good enough knowledge of what you are doing and evaluate situations.
talking about the town that's simply how the early game works. prosperity is randomly generated for all towns at the start and if a town has too much it will starve for a while, this allows rebellions to happen early helping the player getting a settlement and start a kingdom. It also allows some clans to be created to help some faction so that the run doesn't feel the same.
Also once the town is fully upgraded like in the chart i posted you can see that starvation doesn't occur anymore.
You may not like it but it's good, like really good.
They have not announced these changes, clearly they are not convinced or this is just a place holder. I am one of the voices that object to the direction this is going and will remain so because i had to endure hours of helplessness against something i cannot control or fix by my contribution, the main character.
TaleWorld does it many times, things get changed and they forget to say it.
Shops and caravans are tweaked basically every patch to "balance" the economy, yeah they just create a big mess sometimes.
Units may get a little tweak and nothing is said, i don't remember seeing the helmet the Legionary use being nerfed to 47 at any point but it did.
Patch notes, only include major things and are also written by a human, but i agree they should add stuff like this to them and not forget about it. That one is on them.
OTHER THINGS:
Depending on policies prosperity can also rise or decrease.
Food villages and number of bounded villages are also key to prosperity.
The early game can mess some town up for the benefit of the overall gameplay, try starting a new save use cheats to max a town early on and you will see their prosperity rise or not lowering.
Your point about oil presses and wineries being not great for food production is interesting but i don't think it has all the impact you claim. if so then you should run some tests: take away all oil presses from the map and wineries and see if the towns have more or less food.
little spoiler, they probably won't, as the food in the trade hub is just a tiny fraction of what they actually have available, that's why if you put 1K grain in a town you are not fixing them from starving, it's not a real 1K it's more like a 50.
A land lush and green, protected by a natural border to one of it is flanks should be more prosperous not less. So i don't know why you are telling me that it has been always like that and that's fine. No it is not and it needs to be looked at.
This one depends.
In todays era green means food, but irrigation, and land fertility is a factor. Just because it looks green doesn't mean it's fertile. it may have some ivasive insects or animals that at the time were hard to get rigged off. If you really want to find a meaning to this, at the end it's just mainly for balancing.
I don't know how to explain this in a more fair manner, and also 500 hours on a game like this are very little. i played 2,5K and still i don't know many things despite knowing and explaining things that a lot of the playerbase doesn't know. I also am in contact daily with other players who know a lot, so i consider most of what i explain to be up to date.
there is also the possibility of me being wrong, but i don't feel like this is the case as many things can be explained with what i know.