That is the million dollar question - what is the end point? I think it is differnt for us all and perhaps it is an ever moving target for some. Nobody really stays still. We grow older, we make life 'transitions'. Maybe the key is to be happy with the journey?
Transition is not a straight A to B either. They can go in all sorts of directions and people stop off along the way or get back on again, or change tracks.
You can certainly be a girl in a way you want to be, some people manage to be socially woman even if they don't 'pass', some people live part time - one gender at work, but live as the other in all other respects. You can decide it now "I am a girl" and nothing else external changes that. For some people this brings a lot of peace.
I suspect you are right that some, but not all, TS folk stop because they are androgynes and don't know it. We actually have a few members here that transitioned fully then pulled back some of the way when they found it was not right for them.