Did you encounter any other issues apart from the bad documentation? We're considering Sencha Touch for a new project and - as you said - no other framework seems to be as good as it.
Major problem with sencha is it all seems merry initially, then one day you wake up and realize you are in deep shit. Bugs crop up out of nowhere, you WILL have to find work-around solutions.
I heard the official Sencha team is pretty much unresponsive, they mostly concentrate on serving paid clients.
Performance was very poor initially, but its ok now.
Sencha Touch team concentrates so much on iOS, that it is relatively very poor in Android. Just beats the reason to use a cross-platform platform.
But if you are looking for a clean solution, then go native, mobile web still sucks. (I so wish it dint)