Power rating means almost nothing in this game. It's only an indicator and provides no effects.
It is heavily reliant on things that have little impact on a battle. Health, for example, can seriously inflate a Power number without providing much value in most instances.
Power can also be pumped up by stats that have ZERO value to a hero. If a Drac has a bunch of Basic Damage, his power reading will go up. But, he'll get no positive benefit and in fact will suffer from not getting stats that actually help.
So a properly setup hero will destroy a hap hazard hero with much more power.
Then there's the fact that some heros with very high Power ratings plain suck. Dragon Lady and Snap can have huge Power numbers and be basically worthless in a fight.
Finally, there's the deal that some team setups wreck other team setups. 5 Tasty heros versus a Spide, for example. You could destroy a team twice your 'Power' with the right setup.