Maintaining a large player base would help, but wouldn't really discouraged DoS attacks, just make them less common to encounter. If trials was more fun and less frustrating, perhaps it could maintain a larger player base. Maybe to keep it fun, they could focus more on connection quality, and less on matching you with players with a similar number of wins. I don't mind facing better players, but it's certainly no fun matching players across the world that have a horrible connection due to distance. I'm sure there are multiple things that could work together in concert to reduce the frequency you run into people using DoS attacks and keeping trials fun. It's definitely no fun investing an hour or more of your time to be cheated out of the lighthouse by a DoS.