i completely agree with you in the problematic nature of Nietzche's ideal. As you stated earlier,alot of personal struggle is resolnated through ones literature and it is no diffferent for Nietzche as if you read any biography, it would put that his life was pain ridden. he was a very sick all the time and almost blind for writng days or even weeks wihtout break. he pretty much drove himself insane. another issue is the "heart of darkness" example; i think it's important to acknowledge, although the Nazi took nietzche and worped it, the danger of having or being an ubermanchen for beyond good an evil, one must draw power from ones own decision; trust in oneself. it can easily turn out like kurtz who redeamed himself only through death.
another thing is, i belive one of the fundemental and most important aspect of existantialism is creating ones own belief thus although we have different interpretation of Nietzche, regardless of his original intention, it is for us to interpret for outself and try to learn the most from it. As our own definition matters more than his intention in the light of individualistic existantialism. Thus, ultimately, neither of us can prove each other wrong or right as Nietzche's poetic writing, very much impressionistic --like the art of the period-- emphasises the interpretation of oneself (i presume so.. perhaps wrong.. ?). there arethus no "right" answers but better or worse answers. I tihnk your argument is valid and it may be due ot my lack of knowledge in both of these philosophers that we have such dissent; yet i also speculate the underlying difference in our perspective cannot be "proven" wrong but instead we can learn from each other through communication
so keep posting, i'm ready to explore.
**thanks**