Power isn't everything, nor is level, how is "stronger of convoy team" going to be picked. Unless there is, for lack of a better measurement, at least a 30% power difference between the two team members, it just can't be certain. I've had plunders where the second player up actually won, thou few as it might. This is even more attention due to the elemental countering, however minor it is.

Also, 4 convoy and 2 plunder makes the total possible number of plunder and effective convoy equal. Having 3 plunder can, should player be enthusiastic about plunder, end up with many players Qed for plunder and never get any. That's not a good game state. (Granted, this is a significant issue on servers with only 1 or two guild already)