I view Flask as interesting from an architectural standpoint only. It helped me understand Python better. I liked its test suites, use of string imports, and code quality.
When I wanted to get work done, Django did everything. It had a great ORM system, form handling, views, and a template engine.
I can't think of any benefits Jinja2 (Flask's template library) has over Django templates. Maybe Jinja2 performs a bit faster.
SQLAlchemy, while it's awesome (and I do use it a la carte), isn't much better than Django's ORM in the big scheme of things. In fact, the use of the QuerySet object across Django and its third party package ecosystem makes playing with your data a lot easier.
I never had the dream of "microservices" pan out. Most applications I make end up being monolithic more or less, heh. Any non-trivial application I've dealt with outgrown Flask quickly. In fact, they outgrow Django. In a large application, I maintain a lot of code that does't touch the web framework at all.