It's been a while since I did the research before writing the answer you quote, but based on my recollection (and what I know about the science) is that sugar is not required.
Sugar is mostly used to maximize flavor extraction in some cases where a sugary final product is desired, as in traditional production of some liqueurs. But since extracts are not generally "sweetened," there's no sugar requirement.
However, it may serve various functions when present, perhaps including:
- speeding up the extraction
- balancing flavor of the extract (as you suggest)
- slightly changing which flavor components get extracted or their proportions, due to varying solubility in a sugar solution (though I imagine this effect is quite minor except where there is a large amount of sugar involved)
- increasing the amount of extracted flavor overall (this is particularly useful in situations where the ingredients have a high water content, such as fruits; in other cases, the effect is likely small)
A quick web search brings up a number of recipes for the kind of extracts you mention which involve no sugar. So it's definitely feasible.
On a related note, most commercial liqueurs are generally manufactured by steeping the other ingredients in alcohol first, then adding sugar after steeping and straining. (There are various processing and convenience reasons why this is done, and the minor flavor extraction loss is generally not considered significant enough to require sugar to be used in the steep.) So it's definitely possible and common to extract significant flavor without sugar, even if you planned to add sugar later.
Will there be some flavor differences in the resulting extract? Possibly, but the extract should still be fine.