GCs don't see Buck as a man, but Buck sees himself as a man.

GC sees Buck as an adult human female and Buck does the same. As Buck and GC refer to two different things with the letter combination "man" we have to translate it. Buck is referring to having a gender identity, as anyone can identify as anything there is no reason for me to disbelieve anyone's gender identity so I would agree that Buck has the gender identity Buck claims to have as there is nothing that stops women from having the gender identity Buck has.

Other trans men say it's easier to publish their work than under a female name

Exactly, their gender identity had nothing to with it, any female person passing as the opposite sex/using a male name would get the same result as these females, regardless of gender identity.

they will always experience female oppression no matter what

They will experience it at the same level as any female person in their situation. Females who identify as men and don't pass as men will experience female oppression at the same level as other female people who don't pass as men. Females who identify men and pass as men will experience female oppression at them same level as other female people who pass as men. In countries where abortions is banned pregnant females who identify men will be banned from having abortions just like other pregnant females. Identity itself makes no difference.

I was specifically talking about trans men who pass as male.

Then you are talking about looks, and looks are not same thing as identity.

Anyway, we were talking about cisgender gender identities and experiencing female oppression doesn't prove a person would have a a cisgender identity (fetuses who are aborted for being female may have had any gender identity). I personally don't care that you have a cisgender gender identity, your mind, your business. I do take issue that you want to label people without gender identities with false gender identities against their will.