The word futa or futanari is a term I unfortunately see used against trans women and actual intersex people. It is a term which originated in porn and anime to describe someone with both types of genitals, usually though it just refers to someone who looks feminine and has a penis. So it’s no surprise it’s very often used to describe non-op trans women primarily. Because it’s often used in porn it carries strong connotations of sexualization and dehumanization, it reduces the person being called futa to an object of sexual desire and doesn’t respect them as a person.
This term is extremely disrespectful and really has no place being used, especially in reference to trans women. Additionally because of its relation to porn people who use it will almost certainly be seen as chasers.
I want to say this and make it clear. I as a person with an intersex condition strongly resent and despise the idea of someone calling me a hermaphrodite, it is a demeaning term to refer to intersex people as, as well as completely inaccurate because we are not hermaphrodites. The English word hermaphrodite should not be used to describe a human person in any capacity, to do so is wrong from a scientific and logical standpoint but is also wrong as this word carries extreme pejorative connotations when used against intersex people, and it is straight up transphobic when used against trans women.
So yes I maintain that in 90% or more of the English use cases of it, it is indeed a slur and shouldn’t be used. And to describe hermaphrodites it really shouldn’t be used to describe any human person. I know that Japan has had problems with trans understanding and acceptance and frankly I don’t care. If your language’s terms are perjorative due to lack of understanding then use different terms, which from what you said looks like they’re already doing, good on them.