Unfortunately, most devs (and many players) think that guys with boobs are futas. As you say, they properly are hermaphrodites and possess both sets of sex organs. They shouldn't behave like guys or gals.
Futa is broader, and accounts for hermaphrodite women, true, but it also accounts for intersex women without a vagina as well. The main distinction between futa and sissy/femboy comes down to a combination of identity and whether they have any physical characteristics which are alike to the female sex characteristics. Yes, you can have a man with a substantial chest, but futanari is a hentai term, and doesn't really account for the nuances of identity, and instead prioritizes appearances, so to make a character both have a substantial chest and not be identified as futa, you can't really lean into a feminine aesthetic too much.
If you want to explicitly refer to a character with both reproductive organs, the pistil and the stamen, then the term you use is hermaphrodite, if you want to explicitly refer to a character with the secondary sex characteristics of a female (substantial mammary tissue) but only the male primary sex characteristics (penis) then we don't have as much in the ways of good terminology, just compound nouns like dick-girl. If the character has undergone a transformation of sorts to reach that end state, then transfemme could suggest it, but transfemme is actually describing an identity, and not a body, so it's only an implication, and doesn't account for transfemme's who have had their male sex characteristics replaced
Terminology surrounding porn and other sexually explicit subjects is a surprisingly fascinating topic to study
