The levener is baking powder and baking soda. Rhese are cheap ingredients a container of each can last years.

Those mixes are easy to replicate. If the mix changing prevents them from making it from scratch they were never a baker. Anymore than making me making a Mac and cheeses makes me a chef because I added some sliced cheddar.

These mixes were created for convenience. They did not create the concepts behind the end product. They are made with magical difficult to source ingredients.