"Underdog" GAC feat is inappropriate during 3v3

While that may be true for you, it's objectively harder if you have 66% of the opponent's toons instead of 80%. It's also objectively harder in the sense that what really sends squad strength up is not the individual toon, but the synergies. With only 2 toons, there's minimal opportunity for developing synergy. With 4, there's room for plenty of interactions.