The studies cited prove more that gluten free diet foods cause dysbiosis then they prove gluten free diets do. Not to mention the small sample sizes are hardly conclusive.
How about some studies where the participants eat real food and not processed GF junk food, which by the way isn't even wholly GF as per the FDA allowing 9PPM and Spain allows 20PPM of gluten in GF foods.
How about a study that looks at replacing the PREbiotic fiber that is given up when patients go GF since gluten containing foods are the primary source of prebiotics in the Standard American Diet.  Or gluten free diets that focus on nutrient density instead of replacing processed junk with processed junk.
The right kinds of studies matter, and these are not focusing on the right questions if you want to prove that gluten free is the actually problem versus the Gluten free diet choices most people adopt. I propose that a study that compares GF diets that have a focus on healthy, nutrient dense,  and foods with proper prebiotics against a diet of GF substitution foods would come up with vastly different results to the microbiome. I don't think the same species would be lacking in a healthy diet that focuses on replacing the prebiotics that gluten containing foods provide.