How would food production be like without soulcasters? Has Alethkar, for example, grown far beyond what it could (population-wise) without them?
The food question is a great one. As far as the Alethi go, it's more a matter of concentration than raw food production. Shipping is SLOW in Alethkar. It's long, which makes getting between north and south difficult, and the rivers aren't as useful as they are on (say) Earth.
The warcamps, for example, would starve themselves out short order without soulcasters. Supply lines are just not an Alethi strength. Kholinar, while not as big as Scadrian population centers, is also large enough that it depends on soulcasters for some of its food. It could survive without them, though, with northern Alethi food production.
Really, warfare is where they've learned to extend themselves, and depend on the soulcasters. Remember, gemstones in them DO break, so you do still need a ready supply of emeralds. The larger, the better.
Very interesting on the food logistics of Alethkar - I never did quite imagine Kholinar was smaller than say, Elendel, but the technological progress there explains it.
Given how slow food transportation is, I would presume fresh food is a no-go. Are spices and preserved food selling well in Roshar, then? As for population centers, is Kholinar the largest around, or are other places a lot larger?
There's a reason that Herdazian food (which makes soulcast meat taste good) is popular these days.
Azimir is larger in population than Kholinar. Kholinar is big by Rosharan standards, but far smaller than an Earth population center (like London) at a comparable time. The warcamps had it beat by a lot--depending on how you view the warcamps. (As one city, or ten small ones.)
Does that just mean Herdazian food is incredibly spice-heavy, then? Also, why is Soulcast food bland? Is it due to the nature of the object (changing food to food makes it tastier than stone to food), or just because the Soulcaster lacks practice, like Jasnah did with strawberry jam?
Flavorful, rather than spicy. Most western food is already spicy. The Herdazians offer something a little different, and are pretty good with soulcast meat. The portability is also a bit of a revolution.
Soulcasting anything other than the basic Essence requires some innate knowledge and practice. People could learn to soulcast better food, but it would have to be a Radiant with control over the process. The soulcaster fabrials are far more rigid in what they can create.
As for soulcasting - now that is... interesting. So are Surgebinding fabrials more rigid in general? And what of an Honorblade when a non-Herald uses it?
A soulcaster is built to do a certain thing, and can do that certain thing well, but without as much flexibility. It is the difference between having a computer output a picture of a circle--following some inputs such as size and some changes to shape--and having an artist who can draw what you want.