One of the busiest gliding sites in Europe (Lasham) manages perfectly well without ATC even when running a comp, which can involve launching 60 gliders by aerotow within an hour, which means at least 60 launches and 60 tugs landing, plus any glider that comes back for a relight and it's additional launch & tug landing. They might have the winch or winches running as well (they have two Skylaunches)...