Re: aikido vs jiu-jitsu
I practice Aikido, and a little BJJ.
In my experience, there are few options for the full mount, being the use of JJ techniques the most obvious one.
On the other hand I must comment that several fist and finger torsions are not used in general trainning in a BJJ mat. Therfore, depending on how the action evolves, it is possible to think on a nikyo or sankyo or some finger torsion to be used.
The weakest point of grappling fight, of course, is the use of dirty techniques such as biting, eye gouging, and so on.
But letīs not fool ourselves, being on the ground with a ground specialist, such a BJJ figther is a serious problem.