2s use the Image/Feeling center to think "I dont need/feel anything", they seek reassurance in the love of peoples, to meet their need, their consideration, their affection, at the point that they are selfless and forget their own needs.
3s use the Image/Feeling centre to think "I feel good". They are focused on their challenges, pride, glory and success, and are confident in their ability to achieve it.
4s use the Image/Feeling cenre to think "I feel bad". While 2s forget their own needs, while 3s are focused on what they have and their success, 4s are focused on what they have not. They are focused on what peoples have and that they have not, what they lack. And they are seeking for what they lack in every situations, and also how their image could be different, how their feelings, romantic relationships could be more intense. So, this is because of that attention mode that they are melancholic and always focuses on a way to make their image more diffrent, more intense, more unique, mor authentic. Plus, every E types have a hard time to take distance with their coping ressources, so 4s have a hard time to take distance with their melancholy that they often considered as way to make their life more interesting, to feel more intense feelings, wich are more authentic than a simple happiness. At the same time, they see other peoples who seem pretty content with that simple happiness, and then, they feel that they lack something, but since they get that simple happiness, they are again focused on what they have not, and seek something original, dramatic, whatever wich seem always more attractivce than what they have.
So, yes, 4s are driven for authenticity, uniqueness, etc, but the enneagram system don't watch the egg instead of watching the hen like you do, it explain that behaviors of the 4 are coping ressources and that they are primary seeking for love, affection, image, and so, that can totally match with the jugian function Fe.
Anyway your conceptions about Fe and Fi seem wrong. Fi is not more concerned with authenticity than Fe, and Fe is not more concerned with ethic and cooperation than Fi.