Since this discussion resurfaced recently…
…here is my hot take:
KGS is still a larger server than OGS (even though OGS has a larger social network, if you will).
Generally speaking, more games are played on KGS than on OGS, which would seem to indicate there’s still a loyal playerbase that remains despite its decline in the last decade. I have reasonable evidence to support this statement, even though it is quite difficult to ascertain precisely.
So, OGS has been growing since the merge (or even before that), but it’s not quite there yet.