Earlier quoted context omitted.
I was forced to fall on this trap once: a guy has a small Flask app up and running, and he asked for help to implement: an ORM with migrations, an Admin and form validation (among other things that had nothing to do with Django such file parsing). I suggested to migrate the app from Flask to Django while it was small and simple, but he refused for Django is "too big and complicated". OK, then. We ended up creating a…
I like to paraphrase Greenspun's Tenth Law in this context: "Any sufficiently complicated Flask app contains an ad-hoc, informally-specified, bug-ridden, slow implementation of half of Django"
Flask’s marketing of a simple route decorator makes it seem light weight but once you add everything else it becomes Django.