Is google cache also a copyright violation? What about the internet archive? Or do you mean just because they choose not to display certain elements it is a copyright violation? What about just not running javascript?

I guess the op was referring to storing the content which I am not sure if outline is doing. If the save the content and make it searchable then it is kinda violation to take away unique content.

Google cache does exactly that

Google cache does not transform the content.

There's no copyright violation by a browser refusing to load obnoxious css elements... it's more akin to an adblocker also blocking objoxious garbage.