Board Thread:General Discussion/@comment-25926288-20170429134340/@comment-35751112-20180601222115

Presumably, as Gothel is a corrupted tree nymph (so isn't human) and Alice is her daughter (hence only half human), their power comes from a different source than the "human magic" weilded by the Mills family. We can assume that tree nymph magic is stronger than human magic from the fact that Regina was so easily defeated by Gothel - indeed, her magic had no effect on her. Even Rumple with his DO powers didn't try to take Gothel on (although that was possibly because he wanted to avoid doing anything dark rather than lack of strength, we were not told).

It was only Alice (being half tree nymph) who was strong enough to take her mother on and defeat her. Hence, Alice and Gothel would appear to be stronger than the human magic users.