> As I said, any time a Flask app becomes non-trivial, it's a pain
Results may vary. Small teams doesn't mean small apps. You can have 150 models, dozens of screens, caching, background jobs, rate limiting, multiple payment providers, multi-tenancy, public APIs and other features you would expect in a decently sized SAAS app and it's fine. The popular Flask extensions for certain behavior are pretty well maintained. There's also a number of Python libraries that can get used in a Flask app that aren't specific to Flask but are very well maintained like SQLAlchemy and Celery.
I wouldn't say Flask is better than Django or Django is better than Flask but I think you can be wildly successful building an app with either one. It comes down to personal preference. Your post made it seem like Flask is some graveyard of dead libraries and you can't build anything successful with it but that's not the case.