If teams like US, Alumni and Deity are the winners of mixed it keeps the prestige of winning mixed a lot higher than iDevice... I think everyone would prefer being in a team that won Mixed over a team that won iDevice. Mixed is much harder to win than iDevice.
But this thread isn't asking which is tougher to win...it's asking which is more competitive and due to iDevice filled with numerous good teams...compared to Mixed with the strongest GST Team it's obvious iDevice is more competitive.