She has barely been in anything yet and she's in action flicks. Have you seen any action movies? Aside from the rare talents who get drafted to do films (Bale, Hardy, etc.) you're looking at guys like Schwarzenegger, Stallone, Jean Claude Van Daam. Hell Jackie Chan and Jet Li were action stars without a fluent grasp on the English language.
No one is saying she'll be Leonardo DiCaprio, because she doesn't have to be. Gina Carano made a career being a hot action star, I'm sure Rousey could, and Rousey unlike Carano is already a household name. She got billed on the Expendables, granted pretty much everyone in the film was billed, but it's still something. That was back in 2014 or so her stock has risen.
She'd be much better off leaving behind MMA even if she earns less now, she'll earn more long term and more importantly have her health.