Well, that depends heavily on what style of music you like. If you love rock music, you probably think the Rolling Stones are one of the most influential bands in music history. If you love R&B, you probably think the same of the Temptations. However, R&B fans may think the Rolling Stones brought nothing to music and rock fans may feel the same about the Temps. I believe that your impact on the history of music is dependent upon how influential you were as an artist, performer or musician. In this case, Whitney Houston has been tremendously influential on a whole range of pop, rock and R&B singers. For many young female singers today, Whitney was their Aretha or Billie Holiday. I think her importance is limited because the style of music she performs is fairly narrow and because her songs aren't really advancing the artform. But, as a singer, I don't think there is any question that she will always be regarded as a significant figure in music if for no other reason than the influence she had on an entire generation of singers.
Find me one list, Rolling Stone or otherwise that ranks the top popular vocalists ever. Whitney will be on every list. Somebody likes her other than me.
Would rather listen to Etta James or Billie Holliday any day, but I am glad if Whitney is deciding to be a singer again instead of Late Night Comedian fodder, she had too much talent to be remembered as a punchline.
Who cares about a singer not writing her own song or create a new genre when she can sing? I mean, who cares about an Oscar winning actor/actress not writing the plot or creating a new genre in movies? Whitney is like an Oscar winner in music, she is a vocal master that puts the likes of Aguilera/Spears to shame.