Sasuke was beating Itachi in fire ball jutsuyeah no, her clan can have average chakra and hers was stronger than the others. The other interpretation is she had the ability to use yin release to form chains, because she doesn't possess yang release. And Yin isn't a common ability in Asura descendants due to the yin yang split. It is yin chakra possessors that have the potential for powerful chakra as confirmed by Tobirama.
Also, Sasuke even with MS was so far beneath Itachi that he's like a flea before the Uchiha elite.
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