I usually just point them to my fantastic record of 38 Loss - 2 Wins.

I got the 2 wins because the other team didn't have all 5 team mates enter the arena.

Unless at least 30% of the top 20 teams in world is multiboxing, it doesn't matter. The fact that only 1 team has made it isn't enough data to prove anything.

Or if there is a record that multiboxing guarantees a win in arenas.