I'm 8-fixed, and actually, being "vulnerable" (or being seen that way, since I am an image type) is something I resist. I don't like thinking of myself that way. When I find myself in a vulnerable position, I try to rectify that right away. I don't secretly walk around feeling vulnerable (being a 4, sometimes I make a show of it under certain narrow, specific circumstances, but it's basically manipulation when I'm in that state, not true vulnerability).
I dunno how my general demeanor may appear to others--I've certainly been told to show more vulnerability before. But it's not like I walk around feeling constantly vulnerable, and I doubt it's that way for core 8s, as well.