This is such a shitty way to frame it.
I think folk should default to neutral pronouns, especially in trans safe spaces. But phrasing a failure to do so it as “misgendering trans people” is jumping straight to the most absolute bad-faith interpretation.
Then further, saying that anyone who does it is “a transphobe” is way off base. (It reminds me of Contrapoint’s bit about essentialism)
It’s also notable to me that you’re not asking for e.g. any change of policy here. You’re not trying to improve the way this instance is run to discourage folk from using masculine defaults.
You’re using this incident only to wage war against someone you were already in conflict with, and assuming that anyone who steps in and criticizes your behavior is taking sides in that conflict.
Here is some previous discussion on whether to defederate from them due to worries about their moderation capacity (and how it leads to spam/etc): https://lemmy.blahaj.zone/post/1671319