Madonna: This Used To Be My Slayground and Slay A Bow are by all means remembered, but they'd definitely be ICONIC!!1!!!11! today had Madonna not gone out of her way to pay them complete and utter dust for over twenty years.
Mariah: Migrate tbh
Barbra: The good sis Streisand should be remembered for her slayful quirky pop-rock 70s peak (in particular, the immaculate Stoney End album), not for being a Broadway show tunes chanteuse.
Kylie: Literally any song off Body Slaynguage deserves iconic status over Can't Get You Out Of My Head, great as that song may be.
Janet: Rock With U >>> the rest of Janet's own output since 1997.
Amy: Love Is A Losing Game

It pains me to just mention it.