True, only when you have one of the biggest motors already, and that it is fed close to saturation.
Two 15 lbs motors will not make the power of one that is 30 lbs. Now, if you have a 30 lbs motor already and want more power, it might be difficult to find one that does beat two of them. Yet, a 100 lbs motor can beat 160 hp, and that is much more power than three 30 lbs motors are capable of. The logic is that a considerable part of a motor weight is in the support, and the bigger the motor, the bigger the percentage of it can be copper and magnets.