There is a lot of movie miscasts in the history of films, from Judy Garland in "The Wizard of Oz" (who against all odds became an adorable icon in this role) and Deborah Kerr in "From Here to Eternity", to Meryl Streep in "The Bridges of Madison County" and the two male leads (Hanks & Willis) in "The Bonfire of the Vanities". With a bit of luck, miscasts may lead to a career breakout or a hit comeback. So everything is relative in the dream factory too.
I agree about the abovementioned Diana Ross but not the others: there was a pile of production problems and inconveniences in the making of those movies and those actors being the leads weren´t the worst of them. Angelina Jolie playing Colin Farrell´s mum was as laughable as seeing Joan Collins in a blond wig on "American Horror Story"...Agree about the actors from "Interview with a Vampire" with the exception of Brad Pitt and Kirsten Dunst.
Sophia Loren actually did play Cleopatra in one of her early movies, but Taylor did give to Cleo the gravitas and charisma the character needed, independently of how she should have looked. Montgomery Clift falling in love with Anne Baxter (who always looked older than her male counterparts) in Hitchcock´s "I Confess" is quite unbelievable despite his remarkable performance. Actually, every time I see Baxter in anything (including "Hotel"), I can´t help thinking she is lying and hiding something from everyone a la Eve Harrington...so I find her miscast in almost anything else.
Marilyn Monroe was miscast in "Niagara" but no one did care at all because she gave all of her to the role and audiences made it a big box-office hit. Other cases: Anne Hathaway as Catwoman in her Batman movie (and a few of others too), Cher in her Oscar-winner "Moonstruck", Robert de Niro in the "Fockers" saga, Ryan Gosling in "La La Land" (and also a few others), Leo Di Caprio in "Titanic", Julianne Moore in "Hannibal", etc. Anyway, as I said before, this doesn´t mean you can´t enjoy the movie or that it can´t really make a fortune...as odd as it may sound.