No, you can’t presume that. That might make sense if Hollywood Accounting weren’t infamously irrational in all ways that it budgets and (especially) reports profits and losses with an eye toward minimizing residual payments and net profit shares. Your argument presumes that Hollywood pays actresses less than actors because the value added to any given movie’s bottom line by a given actress must be inherently less than that added by a comparable male actor because why would liberal Hollywood manifest such inequities simply because of long-established sexist precedent? That sexist precedent is indeed long-established and deeply entrenched, and a lot of attention is finally being paid to it because it’s not imaginary.
It’s founded on the same principle that gives rise to the ridiculous surprise that so many express in the industry media every time a movie with a mostly female cast does “unexpectedly well” in the box office, like Bridesmaids. Even people who know better still unconsciously undervalue women in movies. And that isn’t based on rational market analysis, which doesn’t really exist in an industry that keeps backing up the Brinks truck to Adam Sandler’s driveway. Rather, it is based on our long-established societal and cultural sexism that undervalues women in every corner of society.