Non-acceptance of the Nicene creed is hardly a "tenuous reason" for placing JWs outside of Christendom. It's a very longstanding and widely held definition of Christianity that JWs, Mormons and a few other "heretical" groups fall outside. It is a definition which has a very long history, and was in no way invented simply to exclude JWs.
In the end there is no correct answer to the issue of whether JWs are Christian. A person's position on the issue tells us more about that person's own views than it does about JWs or Christinaity.
To a JW they are Christian because they believe they follow the Bible, in fact they believe they are the only Christians.
To many Christians JWs don't count as Christian because they don't accept the Nicene creed.
To some liberal Christians JWs may count as Christians because they are liberal and simply don't like excluding people.
To some onlookers JWs behave in ways that don't seem very "Christian".
To some former members JWs are not worthy of the name Christian for a variety of reasons from false teachings to harmful practices.
To some atheists JWs might as well be called Christians because all Christians believe nonsense anyway and have harmful practices, so why single out JWs as non-Christian?
There is no right or wrong answer to the question are JWs Christian? It depends on your perspective.