I like to look at it from a different perspective. The wort correction factor is based on the fact that different sugars (carbohydrates) have different molecular weights. Depending on your grist, mash schedule, composition of sugars in the final beer (unattenuated simple sugars vs unfewntable dextrines), the weight vs refractory index will diverge.
But, for a given style of beer, with similar grist, mash profile, and yeast, the refractive index should be a very valid comparison. So you can think of it as a reading of its own, vs a means to convert to gravity. If anything, the refractive index is less sensitive to alcohol and is a more definite measurement of sugar content, so it's more absolute. If you have a Saison and raise the OG by 10 points, the same FG will actually have much more sugar since it's an overall average of density (high for sugar and low for alcohol).
Brix refractive index isn't a commonly published number, which is why I like to measure as many commercial beers as I can. Comparing your Saison to Dupont or another classic style is very useful, even without converting to gravity.