During their peak they were label the "Worlds Biggest Pop Star" but which one during their peak was the least powerful in terms of "Music Industry Domination" interesting enough 4 of the 5 all had one million debuts...

Taylor.

In order for them to have power they must be able to use it how they like. One of the people you listed doesn't belong.

It's between Taylor and Gaga

The inaccuracy of the first two answers Probably Gaga

Britney, she was only powerful in album sales at her peak, nothing else, unlike all the others listed.

Britney, since she had (and still has) less control of her career than the others.

Beyonce

Britney

Bey or gaga... Prob bey

Flawed logic, Madonna isn't powerful anymore but that doesn't mean that she never was just because she's not at her peak

Swift. The other 4 had massive peaks.

Probably Britney or Adele?

Beyonce/Taylor

Anyway, I'd say Bey.

That has nothing to do with what I'm talking about.