What's your top 5? (taking into account sales, impact, legacy, etc). IMO:

1. Madonna
2. Whitney
3. Mariah
4. Celine
5. Britney

Honorable mentions:
Janet Jackson
Shakira
Beyonce
Barbra Streisand

TITAN.

Pretty much my list.

Madonna

Madonna, Britney, Mariah, Whitney and Barbara Streisand

Britney Spears

Jessie J

Madonna
Whitney Houston
Mariah Carey
Britney Spears
Beyonce & Janet Jackson

Barbra
Mariah
Whitney
Madonna
Janet

Madonna is the most successful female musician ever lived , so her

Madonna
Barbra
Whitney
Celine
Mariah

I guess.

Madonna.

Not Celine Dion
I'd replace her with Nicki Minaj
I'm not even trolling
If you ask people do you know SuperBass they'd say yes but only a few people know My Heart Will Go Only because of Titanic
Nicki didn't need an cliche love story movie for SB to smash

Your list is pretty much it.

WW Adele?

Though that is more a symptom of the fact that music itself is far more global than it was when the above mentioned artists were active.

1. Beyoncé
2. Rihanna
I don't care about the rest.

Um.

Cher? No?

Pre 80s:Barbara, Diana Ross
80s: Madonna, Whitney, Janet Jackson.
90s: Mariah, Beyonce, Britney, Shakira
00s: Rihanna, Lady Gaga

Beyonce is becoming the biggest ever right now it's Madonna and Diana Ross Tina tuner

Madonna, Celine, Adele, Whitney.