Doesn't this technically NERF Stealth in a niche way? Now people with See Invisibility can still see you, as opposed to you being hidden from both mundane and supernatural sight.

It might be better off just poaching the Hide in Plain Sight wording from previous editions.

A shadowdancer can use the Stealth skill even while being observed. As long as she is within 10 feet of an area of dim light, a shadowdancer can hide herself from view in the open without anything to actually hide behind. She cannot, however, hide in her own shadow.
Which also serves the purpose of not turning the mundane into the supernatural in an attempt to make the mundane better, if that makes sense.

If you need "5e simplified text" for the ability, you could word it as such: "If you are standing in dim light or darkness, you may always attempt to take the Hide action even while being observed."