For example, Amla (Indian gooseberries) can be preserved by candying them in sugar, or preserving them in brine and vinegar. However, the candying makes them too sweet and preserving in salt makes them too salty. Not just taste-wise, but also health-wise. Instead, can we use a combination of sugar and salt to preserve them? That would avoid the overload of either sugar or salt. If yes, then how? When applying sugar, they usually advice not to add water. So would that necessitate dry application of sugar and salt? 
I think the hypothesis is incorrect: there are certainly Western recipes for stock that suggest cooking for 24-72 hours, such as here: http://realeverything.com/tutorial-thursday-broth-stock-bones/. Most recipes I find for Chinese white stock in English also suggest cooking only at most 4-8 hours. I have never made these long stocks but the longer cooks are claimed to continue creating more gelatin out of the bones, until the bones disintegrate under mild pressure. That certainly isn't true about bones cooked for 4ish hours, in my experience, so something is happening in the long cook, although I don't have any clear information on how significant that something is. 