I don't think so, I've developed a number of apps with Django on App Engine and, as long as you've developed a bit at the lower level and know the limitations, Django is a very good fit. The guys who wrote Django-nonrel did a very good job, pretty much everything that doesn't do any wild joins will work out of the box.
Overall, I am very very happy with Django on GAE and develop with it, even though I've developed with Flask as well. With microframeworks I generally find that you need to reinvent many of the things that Django already provides.
Your only objection that I can see is really the fact that the ORM joins, so don't. As long as you keep that in mind, everything else is transparent because it's really the same as what other hosts offer (memcache, email, tasks, etc).
Overall, I am very very happy with Django on GAE and develop with it, even though I've developed with Flask as well. With microframeworks I generally find that you need to reinvent many of the things that Django already provides.
Your only objection that I can see is really the fact that the ORM joins, so don't. As long as you keep that in mind, everything else is transparent because it's really the same as what other hosts offer (memcache, email, tasks, etc).