Thank you for your question @marcoferrel!
This is also a good example of a well structured question with good information to begin with.
I see that you are adding 2% gluten as well as 0.01% xanthan gum. Although I may not have specifics for the wheat flour you are using, 52% for this seems quite low to me. Because of the added gluten and xanthan, you are effectively at 50% hydration. For a formula like this I would suggest increasing from 52% to 55% water. To get better emulsification and softness effect from the xanthan, it is best combined with liquid lecithin. An approximate starting point for lecithin is 4% based on the fat, or in your formula 0.2%. Adding mono-diglycerides would also be an option.
Double check processes and consistency. Ensure the sponge is fermented at least 3 to 4 hours, at a consistent temperature between 72-76°F. Too hot or too cold are not beneficial. Check final dough temperatures and final proof time, as well as oven temperature and bake time. All of these will affect softness and staling. For the richness of your formula using sponge and dough, I would usually expect 5-7 days of softness.