If "only" 50 people working on a project used by one million people was unworkably low then every single successful project out there would be doomed. I've certainly worked on things with much worse ratios than that.
> one has to critically assess why a team that loves external contributions has only managed to merge contributions from 1,500 developers over a span of nearly a decade.
External contributions from 1500 developers over a decade is a lot. That is an unusually high number, not a low one, and backs up Flutter's claim to love external contributions.
The fact that this person thinks that they can just magically conjure up dozens of volunteer PR reviewers is wild. Everything about this post makes it pretty clear that they don't have the slightest clue of the scope of what they're trying to do. This feels like one of the standard examples of an ex-bigco person setting off on their own with no understanding how just how much the bigco did in the background to facilitate their job.