https://wikitech.wikimedia.org/wiki/Add_a_wiki#Wikidata says we need to run populateSitesTable.php on all wikis...
I tried to make addWiki do that in https://gerrit.wikimedia.org/r/#/c/339144/ but was told that we already had this. Which we do, kind of, at https://github.com/wikimedia/mediawiki-extensions-WikimediaMaintenance/blob/master/addWiki.php#L234-L242
So one of them is wrong; either we need to make it run on all wikis and the instructions are right, so there's no reason why we can't move it into addWiki. Or we don't need to run it on all wikis, and therefore the instructions are wrong, the documentation on Add a wiki needs updating so we don't need to run it on all wikis, and that patch can be abandoned.
Both can't be right.
And FWIW, when creating new wikis, we tend to add to the dblist, and stage before running addWiki now anyway if that makes any influence