> Are you a native English speaker?
Yes, I am. Born and raised in the US.
There are instances where the term is used in a positive sense, yes, but those are limited in scope. "Superhuman strength" rather than just "superhuman".
"Superhuman" on its own is a term that has long been tightly associated with a wide variety of horrible things. Eugenics, for example.
I honestly think most American English speakers are not thinking about eugenics when they hear that term. I believe you when you say that it has those connotations for you but I think you are in a small minority.
I like superhuman as an adjective, it implies some quality of a man is superhuman, but a superhuman as a standalone item is very frightening as it spells obsolescence for the rest of us ( I guess this is the plot of X-Men )
Without a doubt