And yet that's the way it works. Setting the restriction to "edit=sysop" means editing is restricted to sysops (or more specifically, to anyone with the 'editprotected' right). Setting the restriction to "edit=all" means everyone is allowed to edit.
Compare with message MediaWiki:Apihelp-protect-example-unprotect2/en
https://translatewiki.net/wiki/MediaWiki:Apihelp-protect-example-unprotect2/en "Unprotect a page by setting no restrictions."
If restrictions are set to "all", the page protection is at a maximum, because every possible restriction is in place protecting the page.
I cannot make proposals for a text which I do not understand. Forgive me for not digging through the source code attempting to find out what happens when the message is used and eventually confirmed. :-( It took me already more than half an hour to find the abovementioned message due to translatewiki.net's - erm - limited search capabilities. I had seen it a few days ago, but neither fully remembered its text nor its message key,
I already told you what it means. The restrictions specify who is allowed to take the action, not who is not allowed to take the action. Restricting editing to "all" is effectively not restricting editing since it means everyone can edit it, just like restricting editing to "sysop" means sysops can edit it.
Well, I understood what is meant. I am not a native English speaker. Asking three non-natives whom I just caught on he fly, a group of two and another one, told me that they did not understand what is meant. I only asked them: "Can you tell me what this means: ..." - "thank you"
Thus, the wording is ambigous at least. Likely, we should try to avoid the word "restrictions" since 'restricting to what' and 'restricting for whom' or 'keeping ... from ...' etc. is too uncertain and too easily messed up.