Taken simply as P=EI, you are correct. however 3 phase is different from DC or even single phase AC. Because of the overlap of the phases arranged at 120 degrees current is less than for the same horsepower at single phase. I can't remember the exact factor at the moment. Since current goes down, then multiplied by the same voltage, watts must also decrease. In figuring for the KiloVolt Amp rating of a transformer the factor for 1 phase is 1 the factor for 2 phases (so called split phase) is 2 and for 3 phases it is 1.73. VxAx1.73/1000= KVA for 3 phase.
sufficiently confused?