Tornado is excellent... But Flask is better than excellent. The mental map of Flask is incredible. Tornado is a little hard to grok. Now one may argue that Tornado is hard by choice...to not mask the complexity.
But then we have node..the most hip of frameworks out there. Node's true innovation was not performance, but to simplify the mental model of async. Obviously there's all the callback hell and all..but still.
I'm pretty sure both Node and Tornado have the same mental model of async. Both have callbacks and both have async/await functionality that makes it look more like blocking code.
The main benefit of Node as I see it is that the entire Node community uses the same IO Loop whereas Python's community is fragmented between normal sync code and multiple different IO Loops (asyncio will probably help with this).
