Yeah but not humanity alone. What the series implies is that DEMONS can greatly augment their pre-existing power once embracing human emotions and values, reaching their full potential.
Humanity alone is not enough, it's the ultimate "booster" for demons' power, not a power in itself. Not in the literal/combat-related sense anyway.
Remember I said I like Predator 2 more than the first one? By logic, Danny Glover's character, just another big city detective, would stand no chance against Predator, but he did in the end. He was the underdog that refused to quit cause he knew the city depended on him.
If humanity can give demons a boost, why can't that same humanity, the power of love, of strong will, give Lady a boost? She is flexible, she is fast, she has healing powers to certain extent, and most of all she is damn stubborn and brave... so why not?
@Gel
Yeah, i noticed that. As much as he claims to care about humanity, in the end his attitude ain't that different from Vergil's - they are little ants and he is the mighty god above them.