I have heard that people think oats should be like rice, and that the fifth min is a variety of barley. One of the arguments is that the gluten in oats is just cross contamination from other species.
I haven’t really looked into it much, since I’ve heard b’shem gedolei haposkim that our mesorah is that oats are from the chameshes minim, and I suppose I accept the argument that gluten free oats are just oats without gluten.