> How large is the Flutter team, today? Google doesn't publish this information, but my guess is that the team is about 50 people strong.

I doubt google have even 50 flutter devs in their team. You can easily estimate by checking github pulse:

https://github.com/flutter/flutter/pulse/monthly

https://github.com/flutter/engine/pulse/monthly

Also take into account inflated commits by CI bots: engine-flutter-autoroll, skia-flutter-autoroll, auto-submit[bot], fluttergithubbot, flutter-pub-roller-bot