https://www.mediawiki.org/wiki/Manual:$wgRestrictionLevels:

Note: 'sysop' and 'autoconfirmed' are actually user groups rather than user rights, but are allowed for backwards compatibility. They should be mapped to 'editprotected' and 'editsemiprotected' respectively when comparing against user rights.

I think we should deprecate this kind of backwards compatibility (and remove it in a further version). It causes inconsistency, and 'autoconfirmed' is also a unrelated different user right. Propose to:

1. Change default value of $wgRestrictionLevels to array( '', 'editsemiprotected', 'editprotected' ), also change default value of $wgCascadingRestrictionLevels and $wgSemiprotectedRestrictionLevels
2. Change value of $wgRestrictionLevels, $wgCascadingRestrictionLevels and $wgSemiprotectedRestrictionLevels in WMF settings.
3. Rename e.g. MediaWiki:Protect-level-sysop to MediaWiki:Protect-level-editprotected and MediaWiki:Restriction-level-sysop to MediaWiki:Restriction-level-editprotected
4. Change the output of {{PROTECTIONLEVEL}} (this is a breaking change, must be announced)