MediaWiki:Editpage-head-copy-warn was created to allow moving the warning that was previously shown below the edit window above it, per https://www.mediawiki.org/wiki/Micro_Design_Improvements
This actually makes the warning significantly more prominent than before, which is a good thing in that it'll actually be noticed, but it's pretty in-your-face for something that every Wikimedian understands after a while.
As a further iterative improvement, I would suggest making the warning dismissible (perhaps with a link with a friendly label like "Thanks, got it"). Ideally this should be persistent via the preferences API so it doesn't keep coming back if a cookie expires.
This change requires legal sign-off.