Please hide WN/LN/manga spoilers.
MAL entry, Anilist. The zeroth episode is a spin-off-ish, focusing on Sylphy after the Calamity meeting with Ariel, becoming “silent Fitz”, and struggling with her new situation; as well as the power struggles between Ariel and her brother I-always-forget-his-name for the Asuran throne.
LN Events
Agreed, They also seemingly skipped the entire Ariel fleeing Asura adventure and her dealing with losing most of her loyal supporters along the way. They may come back to that as a flashback scene since it isn’t really relevant until after the Ranoa arc.
Re: Sylphie and Ariel - I think they did a good job at setting up the dynamic of the two and it should lead pretty well into the Ranoa arc for viewers.