Sorry for the late answer.
Consumers spawn every population milestone so consumption is already proportional to population to some extent.
Yes it is.
But don't factories spawn depending on demand/supply, somewhat complementing existing producers and consumers? So, if a consumer consumes more than is currently produced, more suppliars will spawn, and if too much is produced, more consumers will spawn? See, dependance on demands is already in the game without JIT2
I don't think it really counts, and I don't think you think it really counts, so let's skip that idea.
In real life production is mostly limited by demand.
In real life production is mostly limited by demand of customers. Which is what I am saying - replacing customers with consumers is not like in real life.
Apple is a bad example because they use limited supply at release for popularity and to boost demand.
That has nothing to do with what I was talking about, it wasn't about producing stuff, it was about selling them, and the "productivity" of an apple store on release day. It's similar to a toy store the week before christmas, if you like that example more.
A good example would be a crisp factory since they will raise their crisp production based on demand.
But how? Do they have some lever they have to set to "90%" instead of "80%" and their machines magically produce more crisps?
Which timespan are we talking about? I recently was to Weber Hydrauliks, they show a weekly statistic on screen of how many orders they got and how many they should get - most weeks are too subpar, but one or two spike that much higher so it evens out. This is regular for companies and really too short-timed to be simulated in Simutrans.
So what would Weber Hydrauliks do if there were several weeks with a higher amount of orders than expected? Again, first reaction would be to work overtime, maybe even nightshifts - which is costly, but better than losing a contract. But that's not maintainable, so if they really keep getting new orders in, they have to expand. Now surely, they don't have to build a new extension or even a new factory somewhere else, for starters, they can reduce their common room to a quarter the original size - which is what they actually did last year, and would be represented in Simutrans by simply changing the base production rate.
But look - this is exactly what I mean. Your crisps factory will not "just produce more than usual", at least not for long, just as a first response.
There are actually two variables here: Let's say A for average production, and M of maximal production. A factory will try to run at A, but can do M if needs be. If it runs at M for a while, it should expand, so the former M becomes the new A, and M is even higher.
But that destinction does not currently exist in Simutrans. You only have a percentag. Question is: What does it mean?
IF 100% is akin to A, you are right in having shops run at 100% constantly, but wrong in not having suppliers do the same.
IF 100% is akin to M, you are right in having suppliers run lower than that usually, but wrong for having shops running at 100%
So no matter how you see it, both is wrong. Which begs the question why it would be better to be wrong in this way, rather than being wrong by having suppliers running at 100% and shops not - especially since factories are much closer to 100% of what it could potentially do than shops.
Ultimatly the consumers set the demand in simutrans industry model so they have the final say.
Just a side note: This is only true with JIT1 and JIT2, not with JIT0 - which is probably the "original" way the game was played, right? Thus, it's not a "rule of Simutrans" that consumers set everything, it's game mode dependant.
In general: I am not against the idea behind JIT2. I just really dislike that you seem to see reaching 100% for consumers is some kind of goal for everyone, and creating consumers with the intention to not be satisfied even with many suppliers somehow wrong. As a transportation simulator, it makes a lot more sense to "transport away 100% of all stuff produced".
Now you have your arguements for why you think your way is the best, and they are not bad. But everytime you use real life as an example, someone could come and use even more real life to make the opposite point, and everything looks different again. Thus, unless there is a better industry model for how many industries (consumers and producers) are spawned when and where, which can be toggled by enough parameters for creators to do exactly what they want and players to tweak it to their needs - there can't be a single solution that's best for everyone.