Smarter developers than me have spent much time and effort hammering into my thick skull the following idea: one of the most important aspects of a senior developer is the ability to choose the correct tool for the job.

Flask is indeed much simpler, and serves the needs of smaller apps very well. The reason I've stopped using it is because I'm now familiar enough with Django's substantial, problematic learning curve that building a Django project is now just as easy for me as spinning up a Flask app (django-cookie-cutter and wagtail's project init help with this, but they're no replacement for several years of smashing your head against bad Django code). While I love Django, and have derived much utility from the tools it gives me, it's not the solution to all problems, and there are times when Flask makes total sense.

But once Flask's simplicity advantage is removed by experience, I find that it's immensely useful to have (largely correct) opinions on ORM<->DB interactions, templating, settings/config management, form validation, and user authentication baked into the project. For my projects, having these has never cost me anything even if they go unused, and more than once I've gotten myself into the situation of "You either use Django or build Django"

All of the above applies even more so to the specific task of producing a rest API. DRF is, by a large margin, my favorite tool for producing robust, understandable APIs, and I've been lucky enough to never encounter the scaling issues that I've been told (and believe to) exist.