You might have noticed that most mecha teams seem to operate in units of three, when they do operate in coherent units. But why units of three, why not units of four like modern fighter aircraft?
I believe this is more about narrative convenience. Strictly in terms of character interaction, three is the optimal number for showing group dynamics without involving a large group: two and it isn’t a group anymore; four and you might wind up with some redundancy, or a situation where one person is always acting as support. (Five implies a sentai show.)
Perhaps we could note the tendency to form crews of three extends to other shows like Evangelion and Dai Guard (which aren’t always comparable to fighter planes in terms of their missions, but which are still giant mecha.) It goes beyond those, as well: the “three man cell” is the ideal of Naruto, but in practice devolves into three people and an awesome badass who fishes their fat out of the frying pan. In Bleach, Aizen’s rebellion against Soul Society is carried out by a grand total of three conspirators, including him (the other two are Gin and Tousen.) The three of them visit Las Noches and effectively lay waste to the defending army before claiming it for themselves.