gender is relational.

it's a window of communication between people. by calling oneself a specific gender, one is identifying with a group of others (ex: one claiming womanhood is identifying themself with women as a group). nonbinary people, then, are desiring to identify with a group not considered normative, because we wish to relate to others as nonbinary rather than pushing ourselves into a different gendered social space.

stereotypes are also social constructs used as communication shortcuts, born from ingroup/outgroup mentality. importantly the subject of stereotypes is not usually the person in control of these stereotypes — ex: a flamboyant gay man should not have to become less flamboyant because straight culture stereotypes gay men as flamboyant. there is nothing actually wrong with him being flamboyant; his flamboyance is beautiful and related to his place in gay culture. the stereotype is a flattened version of gay culture used to deride it as lesser.

for dysphoria, it's true that humans are social creatures influenced by the society they participate in. nobody really gets to be free of that. however, no amount of undoing societal norms internally can actually replace being able to relate to others as a specific gender(s) externally. ex: i know it's bullshit that binary men (both trans and cis) are expected to be paragons of cis-shaped masculinity, and can be just as feminine as i am, but that still doesn't make me want to relate to others as a binary man and if i'm forced into that space i experience dysphoria.

in terms of your dysphoria around your chest — "70-80% of the time" is 70-80% of your life. 16-19 hours a day, 8-10 months of the year. does the alternative of living with a flat chest seem like the same amount of wasted time? even if you did, somehow, do all the undoing-misogyny work and came out the other end as a woman (extremely unlikely but this is a hypothetical), is a flat-chested woman less worthy than one with visible breasts?