Are they

Britney Spears, Beyonce, Lady Gaga, Adele and Taylor wift ?

yes

replace taylor with rihanna tho

You forgot Mariah and Madonna, imo.

I meant new artists obviously and no neither Madge nor Mariah had more impact than any of those. The rise of a superstar alone is huuge impact and both of those happened for Madge and Mariah years before...

I know Britney debuted in 98/99 but yeah most of her impact was from 2000 onwards.

I'd add Mariah to the list.

Beyonce/Britney
Amy
Gaga
Aaliyah.

Yes

Where is Katy Perry?

Yes

Britney
Beyoncé
Gaga
Xtina
Katy

However, Madonna, Mariah, Janet and Whitney's impacts are still more influential in the girls this generation than basically all of these newbies. Shania too in the country genre

Britney, Beyoncé, Gaga and Adele are the only four worth a mention imo.

Britney Spears.

In no order:
Lady Gaga
Katy Perry
Rihanna
Taylor Swift

By far.

HMs:
Christina Aguilera
Avril Lavigne
Iggy Azalea
Miley Cyrus
Kesha

yes

.

What's Taylor's impact though? She tried it with Spotify, got a few headlines, but Spotify only got stronger.

This.

Beyonce and Britney

Britney
Beyoncé
Rihanna
Gaga
Katy

Madonna and Mariah too if you consider artists from 80's / 90's tho.

Gaga

Beyonce

Britney

Mariah - if applicable

Adele

Beyoncé
Rihanna
Gaga
Adele
Taylor