I didn't like this scene at all. It was just fan service. There's no way Arya progressed this much. It certainly hasn't been shown in prior seasons. They need to do better if they wanted this to be the slightest bit believable.
But kudos to Gwen and Maisie on learning those moves. I know the stunt doubles played a big part but they impressive none the less. That dagger spin in particular by Maisie was nice and her using her left hand because she knows Arya is left-handed should be commended.