F-16's and Pylon Racers are intended to go fast. Pattern planes aren't. When I went to my first pattern contest many years ago, I questioned why all the planes had blunt trailing edges, and was told that it was to improve response at low speed. Since then, I have also heard the flutter reason. The reason I have heard that makes the most sense to me is that it makes the plane draggier without affecting airflow over the flying surfaces to assist braking on the down lines.