If I think a hammer looks nice but someone informed explains that it is designed in such a way that the head will tend to fly off, I find that very instructive. The many broken spatulas on github are also instructive.
If you want a pre-built admin, Django provides for a different need, yeah... but if the needed stuff is in the large overlap between Django and Flask, you can't just say "different needs" because you are considering competition to satisfy the same needs. (For example, Flask is promoted for HTTP APIs, but Django also has some good packages for putting together HTTP APIs, so that it is hardly clear that Flask would always be the better choice for APIs).
Most of the argument (here as in emacs vs. vim) is in matters of taste or philosophy - or a dead heat between valid technical concerns. tastypie or Flask? I submit that it matters more what makes you happy and productive, so that it is entirely valid to choose Flask, or Django, or both. After all, it is your life you are spending on all this, you should be happy. If you hate emacs, there are alternatives.