This has been my experience as well. I've been working on a solution[1] in the form of an optional-batteries-included framework built on top of Flask and SQLAlchemy (inspired by Symfony). After about a year of work, it's currently around MVP status and (biased I) thinks it's turning out pretty awesome - the docs are the biggest thing still needing improvement (working on it!).

If you or anybody else is interested, I'd love any feedback! (good or bad :)

[1] https://github.com/briancappello/flask-unchained