It is actually a huge problem for some people. Our family has a very close friend who has Celiac disease (an intolerance for gluten). The only one of the 5 Minim that is gluten-free is oats. However, because some dispute oats as 5 Minim, celiacs who follow this have no way to ever make Hamotzi (Matzoh on Pesach is a huge problem). So the vast majority, if not all, celiacs in the world assume that oats are really one of the 5 Minim and don’t worry about recent Ta’anas against this.
I think the whole proof about oats is wrong anyway. They claim that gluten content is what is Machmitz and therefore, by definition, something without any gluten cannot be one of the 5 Minim. But the Mishnah in Challah (and other places) has the Machlokes between the Chachamim and R’ Yochanan Ben Nuri about whether or not rice is one of the 5 Minim. The Yerushalmi there asks that they should test if it is Machmitz. The Gemara says they did and the Machlokes was whether the experiment resulted in Chimutz or Sirchon. These Poskim explain this Gemara as saying that rice has a minimal gluten content but not enough so it’s a Machlokes, while oats with no gluten at all are Vaddai not one of the 5 Minim. The issue with this is that rice has no gluten at all also. So it’s very hard to say that Halachic Chimutz is tied directly to gluten content. For that to be true, R’ Yochanan Ben Nuri would have to have such a drastically different definition of Chimutz than the Chachamim, and if so it would be incredibly unlikely that rice is the only thing they dispute. Oats have many of the same properties as the other 4 Minim (aside from gluten) and react much more similarly to those 4 when mixed with water than it does to rice.