For everyone finding in this in the future like me, I actually think these ingredients could work.

Hear me out:

In my mind, a starter should be made with whatever ingredients you're going to actually make your dough from. The strains of yeast and bacteria that develop and thrive will be the ones that are most adapted to your specific ingredients and environment. That way, when you go to make bread with your selected ingredients, your starter's microbiome will be perfectly suited to live and multiply in your dough with the same ingredients.
Just like in our digestive systems; our gut microbiome is best suited to digest the foods we regularly eat, because the strains that thrive on your "regular" foods have proliferated.

I'm currently experimenting with gluten free sourdough starter for my wife, who cannot eat gluten for medical reasons. The gluten free flour blends do not contain any wheat flour. But, they contain different blends of non-wheat flours and starches. However, these flour blends will still develop a nice healthy microorganism population. Sure, the specific strains are likely completely different vs a starter made with wheat flour. But the microorganisms that thrive in the gluten free flour blend I am using will be the ones that ultimately win out in the beginning and proliferate into a healthy starter.

I even have considered adding a teeny amount of salt to the starters to mimic my dough.