Perhaps the max power level of a team should be set at less than 18. This might prove more interesting as you would be forced to have a limited number of rank 3 units...say two or three. Or, you could have four rank 3's and two rank 1's etc. Not only would this expand the strategic possibilities, but it would allow more players to obtain a top-tier build in a reasonable amount of time.
This also goes hand in hand with the idea of only allowing 'max-power' builds to take part in ELO ranking and stats. Seems like that is the only way to have a fair playing field.