Now that I see what you are doing, your approach seems to make sense.
Under normal circumstances when yeast is used, 5% sugar would eventually be broken down to simple sugars to feed the yeast, and whatever sugars remained after the yeast is fed would be available as residual sugar to contribute to crust coloration at the time of baking. How much sugar is consumed by the yeast would depend on the amount of yeast and also on the duration of fermentation and the temperatures at different stages, including during fermentation. Also, at 5% sugar, that amount may have an osmotic effect on yeast and impair its performance by leaching out yeast cellular fluids.
Absent yeast, and using a chemical leavening system instead, one of the dominant effects of sugar, and especially at 5%, is to retain more of the moisture in the dough. The reason for this is because sugar is a hygroscopic substance (it attracts water from its surroundings). What other effects the sugar will have will depend on the window in which the dough is made and eventually used. Forgetting for the moment the effect of 5% sugar on flavor and taste (sweetness), the other notable effects of sugar is on crust coloration. If the window for the dough is short prior to using, then the primary additional effect of the sugar is crust coloration. And the crust coloration in this case will most likely be due to the caramelization of the sugars. Normally, one would expect some Maillard reactions but if the window for the dough is short before using, there may not be enough time for the added sugar to be broken down into simple reducing sugars to participate in the Maillard reactions. There are some simple sugars in the flour itself, which are normally used to start the fementation of the yeast (when used), but they may insufficient to make a big difference in the color of the final product.
So, if I had to guess in your case, 5% sugar should give you a tender crust (and even more tender with 3% oil), sweetness, and crust coloration because of caramelization of the added sugar and some Maillard reactions. There will also be coloration and taste effects through denaturing of the protein during baking.
If we strip out everything but for the amount of sugar, on the assumption that everything else will be equal, I would say that the dominant impact of the added sugar is in increasing the tenderness of the finished crust and also increased crust coloration.