>if the grandma's secret receipe is industrial cake mix, I don't know how much of a secret receipe it is

There are a few interesting paragraphs on it in the book "On Food And Cooking: The Science And Lore Of The Kitchen" (2004) by Harold McGee[0]. (p555)

>Modern American Cakes: Help from Modified Fats and Flours Beginning around 1910, several innovations in oil and flour processing led to major changes in American cakes. The first innovation made it possible to leaven cakes with much less work. The hydrogenation of liquid vegetable oils to make solid fats allowed manufacturers to produce specialized shortenings with the ideal properties for incorporating air quickly at room temperature (p. 557). Modern cake shortenings also contain tiny bubbles of nitrogen that provide preformed gas cells for leavening, and emulsifiers that help stabilize the gas cells during mixing and baking, and disperse the fat in droplets that won’t deflate the gas cells.

>The second major innovation was the development of specialized cake flour, a soft, low-protein flour that is very finely milled and strongly bleached with chlorine dioxide or chlorine gas. The chlorine treatment turns out to cause the starch granules to absorb water and swell more readily in high-sugar batters, and produce a stronger starch gel. It also causes fats to bind more readily to the starch granule surface, which may help disperse the fat phase more evenly. In combination with the new shortening and with double-acting baking powders, cake flour allowed U.S. food manufacturers to develop “high-ratio” packaged cake mixes, in which the sugar can outweigh the flour by as much as 40%. The texture of the cakes they make is distinctively light and moist, fine and velvety.

>Thanks to these qualities and to the convenience of premeasured ingredients, packaged cake mixes were a great success: just 10 years after their major introduction following World War II, they accounted for half of all cakes baked in U.S. homes. The very sweet, tender, moist, light cake became the American standard; and hydrogenated shortening and chlorinated flour became standard kitchen supplies for cakes made “from scratch.”

>The Disadvantages of Modified Fats and Flours Hydrogenated vegetable shortenings and chlorinated flour are very useful, but have drawbacks that lead some bakers to avoid them. Hydrogenated shortening does not have the flavor that butter does, and has the more serious disadvantage of containing high levels of trans fatty acids (10-35% compared to butter’s 3-4%; see p. 38). Chlorinated flour has a distinctive taste that some bakers dislike (others find that it enhances cake aroma). And the chlorine ends up in fat-like flour molecules that accumulate in animal bodies. There’s no evidence that this accumulation is harmful, but the European Union and the United Kingdom consider the safety of chlorinated flour unproven, and forbid its use. The U.S. FDA and the World Health Organization consider chlorinated flour a safe ingredient for human consumption.

>Manufacturers are addressing some of these problems and uncertainties. For example, the effects of flour chlorination can be approximated by heat treatment, and vegetable oils can be hardened without the production of trans fatty acids. So it’s likely that cooks will eventually be able to make high-ratio cakes with less questionable ingredients.

[0] https://openlibrary.org/works/OL4110479W/On_food_and_cooking...

Note that today, one can easily find cake flour that isn't chemically bleached. Also, shortening manufacturers have gone to fully-hydrogenated oils, rather than partially hydrogenated, to reduce the amount of trans-fats. But some are still using palm oil, so it's not a total win.