I really don't see how Serena being the face of US tennis matters so much
Only one of the Slams happen in the United States, most of the both tours happens overseas
And Serena doesn't have a individual contract with the WTA nor is she on the same tour as men.
I do believe that of all sports the prize money between the men and women, especially the champions should be closer. But for other reason, especially in slams, maybe men should get a bigger cut overall best the do more work.
Edit: There might be some where completely equal is cool.
In other joint events, there are other reason why Joker winning would put more in his pocket than if Serena won it.
Just saying "Serena should be paid the same" is kinda short sighted
Plus Serena probably makes more in endorsement money than most men too