I think there are occasions where the Stewards use the local group. For example, if a user group does not exist on Meta, the local Steward group must be used to add users to it.

called in CommonSettings.php:

Process group overrides
$wgGroupPermissions['steward' ]['userrights'] = true;
$wgGroupPermissions['bureaucrat']['userrights'] = false;

Exactly what @JJMC89 said. Stewards need this group.

On some (few) cases we needed use the local 'steward' user group in order to change permissions. The Meta Special:UserRights interface only works with rights that exist on Meta, so remote non-Meta-Wiki permissions (such as, e.g. the enwiki 'researcher' group that no local group can add/remove) can't be changed through Meta if they do not exist there (cfr. T14518).

Are there any other use cases other than this? If there're no other use case this should be reopened with a blocking task.

@Ammarpad Unless there are other reasons not to do it, this should be revisited after the subtask is resolved.

In T252814#6138537, @Bugreporter wrote:

Are there any other use cases other than this? If there're no other use case this should be reopened with a blocking task.

I'll search for others. Also, I'm not saying that stewards as a local group need to be removed from the MediaWiki software entirely, only from the WMF default configuration. (after edge cases have been sorted out) For non-WMF wikis, the local steward group can make sense.

MediaWiki itself does not define a "steward" group.

In T252814#6141083, @Bugreporter wrote:

MediaWiki itself does not define a "steward" group.

Okay, so don't have to worry about that.

Turns out there are quite some groups that don't exist on meta:

abusefilter: arwiki, azbwiki, be-x-oldwiki, cawiki, enwiki, enwikisource, eswiktionary, fawiki, frwikibooks, frwiki, frwiktionary, hiwiki, jawiki, ltwiki, ltwiktionary, newiki, nlwiki, nowiki, plwiki, rowiki, ruwikisource, urwiki, zh-yuewiki
abusefilter-helper: enwiki
arbcom: cswiki, fiwiki, nlwiki, ruwiki
autoeditor: bewiki, cewiki, ruwiki, ruwikiquote, ruwikisource, ukwiktionary, vecwiki
autoreview: alswiki, arwiki, bewiki, bnwiki, bswiki, cawikinews, cewiki, dewiki, dewikiquote, dewiktionary, elwikinews, enwikibooks, enwikinews, eowiki, eswikinews, fawikinews, fiwiki, hewikisource, hiwiki, iawiki, idwiki, iswiktionary, kawiki, lawikisource, mkwiki, plwiki, plwikisource, plwiktionary, ptwikibooks, ptwikinews, ptwikisource, ruwikinews, ruwikiquote, ruwiktionary, sqwiki, tawikinews, trwiki, trwikiquote, ukwiki, ukwiktionary, vecwiki, zh-classicalwiki
autoreviewed: mkwiki
autoreviewer: enwiki, ptwiki, zhwiki, zh-yuewiki
botadmin: ckbwiki, fawiki, frwiktionary, itwiki, mlwiki
closer: ruwiki
copyviobot: enwiki
curator: enwikiversity
editor: alswiki, arwiki, bewiki, bswiki, cawikinews, cewiki, dewiki, dewikiquote, dewiktionary, elwikinews, enwikibooks, enwikinews, eowiki, eswikinews, fawikinews, fiwiki, hewikisource, huwiki, iawiki, idwiki, iswiktionary, kawiki, lawikisource, mkwiki, plwiki, plwikisource, plwiktionary, ptwikibooks, ptwikinews, ptwikisource, ruwikinews, ruwiki, ruwikiquote, ruwikisource, ruwiktionary, sqwiki, tawikinews, trwikiquote, ukwiki, ukwiktionary, vecwiki, zh-classicalwiki
editprotected: eswikinews, ptwikinews
eliminator: fawiki, jawiki, ptwiki, urwiki, viwikibooks, viwiki
engineer: cswiki, ruwiki
eventcoordinator: enwiki
eventparticipant: zhwiki
extendedconfirmed: enwiki, fawiki, jawiki, kowiki, viwiki
extendedmover: enwiki, enwiktionary, urwiki
facilitator: frwikinews
filemover: bnwiki, bnwikisource, commonswiki, enwiki, hiwiki, newiki, ruwiki, ruwikivoyage, shwiki, ukwiki, urwiki, zhwiki
flow-bot: arwiki, arwikiversity, bswiki, cawiki, cawikiquote, commonswiki, cswiki, elwiki, eowiki, euwiki, fawiki, fiwiki, frwiki, frwikiquote, frwikisource, frwikiversity, frwikivoyage, frwiktionary, gomwiki, hewiki, idwiki, kabwiki, kkwiki, lvwiki, nowiki, orwiki, pawiki, plwiki, ptwikibooks, ptwiki, ruwiki, species, svwiki, tewiki, urwiki, viwikisource, wawiki, wawiktionary, wikidata, zhwiki, zhwikisource
founder: enwiki
gwtoolset: commonswiki
image-reviewer: commonswiki, fawiki
interface-editor: azbwiki, ckbwiki, elwiktionary, huwiki, pswiki, ptwiki, trwiki, urwiki
machinevision-tester: commonswiki
mediasearch-tester: commonswiki
mover: itwiki
noratelimit: dewiki
propertycreator: wikidata
researcher: enwiki
reviewer: alswiki, arwiki, bewiki, bnwiki, cawikinews, cewiki, ckbwiki, dewiki, dewikiquote, dewiktionary, enwiki, eowiki, eswikinews, fawiki, fiwiki, hewikisource, hiwiki, iawiki, idwiki, iswiktionary, kawiki, lawikisource, mkwiki, newiki, plwiki, plwikisource, plwiktionary, ptwikibooks, ptwikinews, ptwikisource, ruwiki, ruwikiquote, ruwiktionary, sqwiki, tawikinews, ukwiki, ukwiktionary, vecwiki, zh-classicalwiki
rollbacker: arwikibooks, arwikinews, arwiki, arwikiquote, arwikisource, arwikiversity, arwiktionary, azbwiki, azwiki, bnwiki, bswiki, cawiki, cewiki, ckbwiki, commonswiki, cswiki, enwiki, enwiktionary, eswikibooks, eswiki, eswikiquote, eswikivoyage, eswiktionary, fawikibooks, fawikinews, fawiki, fawikiquote, fawikisource, fawikivoyage, fawiktionary, fiwiki, frwiki, gawiki, guwiki, hiwiki, idwiki, itwikinews, itwiki, jawiki, kkwiki, kowiki, maiwiki, mlwiki, newiki, nlwiki, orwiki, ptwiki, quwiki, ruwikinews, ruwiki, ruwikiquote, ruwikisource, ruwikivoyage, ruwiktionary, scowiki, shwiki, simplewiki, simplewiktionary, siwiki, skwiki, srwikibooks, srwikinews, srwiki, srwikiquote, srwikisource, srwiktionary, svwiki, svwikivoyage, tawiki, ukwiki, ukwikivoyage, urwiki, viwiki, viwiktionary, wuuwiki, wikidata, yowiki, zhwikinews, zhwiki, zh-yuewiki
suppressredirect: cewiki, ckbwiki, ruwiki
templateeditor: commonswiki, enwiki, enwikivoyage, enwiktionary, fawiki, hiwiki, huwiki, newiki, rowiki
test-sysop: betawikiversity
trusted: huwiki, kawiki
trusteduser: frwikinews
upwizcampeditors: commonswiki, rowiki
wikidata-staff: wikidata

@AlexisJazz so basically the "bureaucrats" group is "built in" and normally gets full userrights access, but on WMF wiki's this wasn't desirable - so the custom group stewards was made to replace it.

For most of the groups on your list above, some other existing local group that has members has access to manage the group locally so it's fine they don't exist on meta.

I still think this should be WONTFIX/declined: I recently used the group at el.wikinews (https://el.wikinews.org/wiki/%CE%95%CE%B9%CE%B4%CE%B9%CE%BA%CF%8C:%CE%9C%CE%B7%CF%84%CF%81%CF%8E%CE%BF/rights), and I'm pretty sure it's also used somewhere else. It is rare, but still used. This can be also useful even after the userrights issue would be fixed: private wikis don't have global rights applied, yet rarely steward intervention would be required at some custom group, or to do bigdeletes.

In T252814#6474886, @Urbanecm wrote:

I still think this should be WONTFIX/declined: I recently used the group at el.wikinews (https://el.wikinews.org/wiki/%CE%95%CE%B9%CE%B4%CE%B9%CE%BA%CF%8C:%CE%9C%CE%B7%CF%84%CF%81%CF%8E%CE%BF/rights), and I'm pretty sure it's also used somewhere else. It is rare, but still used. This can be also useful even after the userrights issue would be fixed: private wikis don't have global rights applied, yet rarely steward intervention would be required at some custom group, or to do bigdeletes.

Works for me. Should I close it myself?