Thanks for gathering some data here. Very insightful and it confirms some suspicions I've had. I'm one of the people that is no longer creating pull requests for Elastic. I was never a big contributor and I only did a handful of small PRs. But all little bits matter and I was OK with doing that under the Apache 2.0 license and putting my time in and doing my small part. That's not a thing for me anymore. I charge money for commercial software development.
In practical terms, I now have to worry about supporting both Elastic and Opensearch as a consultant (always looking for new customers to help, if you need some advice) and I can't really recommend people stick with Elastic with a straight face either because Opensearch really is a decent alternative and increasingly the default for new users; as I have noticed with my own customers.
I maintain a Kotlin client for Elasticsearch and I have started work on making that work for both Elasticsearch 7, 8 and Opensearch; something that is complicated by the fact that Elastic intentionally made sure their Java client (which I depend on) no longer talks to opensearch. They also deprecated it and introduced a completely new one recently. And of course the recently released Elasticsearch 8 complicates things with a few new features, compatibility breaking changes, etc.
On top of that, Opensearch is starting to get its own features or alternatives to Elastic-only features. I agree that the momentum is still with Elastic but it is not the case that Opensearch is a dead fork. I know of several people that quit their jobs at Elastic because of the license change and that are now working on Opensearch or on Opensearch plugins. It will be interesting to see how the two forks evolve.
IMHO, the license change is long term a mistake for Elastic. They've cut themselves off from open source contributors who can still contribute to making Opensearch, Lucene, or Solr better. So, that's long term not going to be helpful. Elastic has always leaned on opensource heavily for contributions and hiring. A lot of their early hires came from the Lucene community and the many researchers contributing to that and later from people contributing to Elasticsearch. Additionally, a lot of value gets added to the ecosystem by OSS plugins. The authors of those now have to choose between Opensearch and Elastic. That's long term not good for Elastic as a lot of cutting edge stuff usually starts in the plugin community.
I don't necessarily like what Amazon did but I do think they did it the right way from the point of view of creating a credible alternative. And I think that the way Elastic responded to that is throwing out the baby out with the bathwater.
Perhaps the most striking statistic is that the total number of PRs for both combined declined: everybody loses. IMHO, they should just roll back the license change and grow their community rather than fragmenting and shrinking it. Amazon is going to get some of their customers either way. I actually think the fork is working out better for Amazon than it is for Elastic currently. It was a mistake. Amazon is not the most likely steward of open source. But stranger things have happened. Take MS in recent years for example. It's a sound business strategy to not piss off OSS developers. Elastic would do well to take note of that.