I'm a relatively healthy 8, I can assure you that not all 8s are "sensitive underneath, selling confidence". I'm genuinely confident and strong. Here's what make me confident :

I fear of being controlled. What this actually means is "I obey my wills over anyone else's, and no one else's will should surpass mine unless I'm convinced to".

An enneagram coach once said 8 is like being god to themselves, they care and focus on their wills most, they want their wills to come true which I agree to a very high degree. Which is also why I love to own power ; money, social status and other resources. It gets me what I want and put people away from my path.

Now recall all other types' fear. Fear of losing friends, missing out, not loved, unworthy. I just simply don't have that. If I love my wills the most, why would any useless feedback (not constructive) should affect? I'm most important here, how is anyone suddenly having more importance in my life? Doesnt make sense. I decide who should be my priority, what kind of changes worthy to be done from my side.

Heck, want to leave me because I'm overweight? Their loss. I'm happy with me and it's not like anyone die from my weight. Obviously it is their own issue,not mine. But say if a family or partner have issue, I'm sure will listen them most because I know they aren't some toxic strangers.

The key here is, as long as I'm not being a jerk I'm sure I can do as I please. I'm also sure other types can be this confident but perhaps not like our level, because deep inside, people are still tied to their fear until they completely let go. Which is really a huge change.