Power Whip's damage is 70 with a cooldown of 2.8s (70/2.8 = 25dps*1,25 = 31,25dps with stab).
Solar Beam's damage is 120 with a cooldown of 4.9s (120/4.9 = 24,5dps*1,25 = 30,6 dps with stab).
So lets say you are analyzing one Ivysaur to attack. The fast attack for both is Razor Leaf and you already have the energy to use the charge attack (its 100 energy for both). Razor Leaf's cooldown is 1.45s.
For RL/SB: you use a SB and do 120 damage for 4.9s.
For RL/PW: you use a PW and do 70 damage for 2.8s (4.9s-2.8s = 2.1s so you can use one PW and one RL while you only use one SB). So it will be 70 damage of the PW + 15 damage of the RL, so 70+15 = 85 damage in almost the same time the other Ivysaur hit 120 damage with only one SB (120 SB > 85 PW+RL). Even if the RL/PW could hit one more RL, it would be 100<120. So DPS is only one parameter, you cant classify movesets only based in that.
If you want to analyze movesets to Defense, you need to consider the charge attack's cooldown+2s cuz of the AI, and 1.5s minimal cooldown for fast attacks so you repeat the maths.
Got it?.