By my reckoning, Nightmare Moon is powerful (control over the moon and eternal night is no small feat) but does not use her power well to her advantage.
Chrysalis doesn't seem all that powerful to me (basic tricks in magic, shape-shifting, being able to feed off another's strength is her best trick), but she knows how to use her abilities to greater potential, making her one of the smarter (and more dangerous) cartoon villains I've seen.

Implying Nightmare Moon is weak.