I'm perfecting my recipe for a sourdough brioche, but my sourdough baby is still a bit hard to handle

Making the dough entirely out of sourdough makes leavening very inconsistent, especially since I try to feed the sourdough just what I'll be using for the week (38 gr & 38 gr of whole-wheat and water, every Monday and Friday, and I leave it to digest for a couple of hours in a proofing box)

I'm trying to see how little dry yeast I can add so that leavening is consistent but that it can still be considered sourdough (especially nutritionally since I live with diabetic ppl)

Rn I'm using 1/16 tsp of dry yeast and 150 gr of sourdough per 200 gr of flour. The leavening is just right and it makes some beautiful loaves, but the bread tastes too much like normal bread and has none of the sourdough's taste

Can it still be nutritionally be considered a sourdough at this point? Or is the dry yeast doing all the work?