“grind some oats into flour, try to make a loaf of bread out of it, and get back to me.”
If you start relying on what you can produce or replicate from the torah, (to test out what has been previousely set down as halachah) you will be throwing out a LOT of torah. Many, many things that the Gaonim have said don’t seem to fit with our modern day understanding of anatomy and physiology but we don’t throw that out do we? They also stated that cheese can only be made out of milk from kosher animals yet you can find porcine cheese. And even examples of human milk cheese. the point is that even if our scientific testing doesnt corroborate what the halacha is we don’t throw it out. Vastly greater torah minds have seen fit to include oats in the count of chameshet minei dagan.