I understand your concern. I, too, view humanity as but a certain segment of an evolutionary process and, hopefully, not an evolutionary dead end.
But "transhumanism" is what this particular movement of delusional tech-weirdos is called at the moment. As you say, by choice of its own members.
That's why we'll have to stick with it for the moment and find a better term for the kind of immanent transcendentalism that is actually worth considering.