The only time that cost performance info would be useful is during Arena events so DPS isn't necessary. You would judge a unit by their speed rating, their damage per deploy point and their skill. Unfortunatelly, the damage formula is not really known at the moment and seems to change for each event so figuring out how a unit compares to another isn't very precise.
You'd think that with the amount of time the Japanese had with the game, they would have figured out each and every unit's DPS. I just think that since they take their gaming so seriously, they wouldn't omitting something as crucial as DPS. Though I could be wrong and we haven't found where they kept that info yet.