Idk why people are surprised. Taeyeon has never been a bad dancer. She's always been precise with great timing and very few misses (trust me, I've been a SONE for over a decade). She does lack the power that the main and lead dancers have, but she's nowhere near bad. She's never stood out as a worse dancer than her any members since debut. Just look at ITNW remix.
i think she usually doesn't show of her dancing skills bc she has to sing those high notes, so she has to save her power. i don't know exactly, just my opinion😅