Lately, I've been using Flask on the back-end, and React on the front-end.
As far as building APIs goes, Django Rest Framework provides so much. I find myself reinventing a lot when I use Flask vs Django + DRF. Just my 2¢.
I work on Flask stuff on purpose, because it means in the future I'll have more Flask work...
Flask is much more pythonic than django.
In fact, go look at Django's website/documentation, they don't have a hello world or a quickstart, they have like a 10-page tutorial to build some frankenstein nonsense, Flask's homepage has a 5 line application! That's how Python is supposed to be.
The more flask in the world, the better.
edit: now I've read some other people here saying Django gets easier after you use it, or it's gotten simpler... Flask is easy the first time you use it, and it's always been simple. Pythonic. End rant.
Flask actually has a tutorial just like this in the docs [1].
I think you should give Django a chance to be able to compare the two frameworks in these kinds of aspects.
For more serious projects, we use Flask for big commercial products and work and it's very good. Unlike some other tools, what I like about it is that it's very easy to look at the code in a Flask project and immediately understand what is going on.