I totally agree that's the best metric. I totally disagree with your characterization of Spark. I showed up on the mailing list, said "hey, here's some stuff

I totally agree that's the best metric. I totally disagree with your characterization of Spark. I showed up on the mailing list, said "hey, here's some stuff that was useful for me, let me know if it's useful for anyone else." A committer said, "cool, send a PR". Couple of rounds of code review and it was merged. Later on, bigger features required a lot more discussion, but as long as I was willing to follow up, I got my changes in. Spark has on the order of 1,000 contributors. I'd call that a "real" open source project.