Final answer:
The topic sentence 'Although writers do not have fixed salaries, entrenched stereotyping results in a substantial pay gap between male and female authors' best encapsulates the disparities and systemic issues leading to income inequality in the publishing industry.
Step-by-step explanation:
The most suitable topic sentence to unify the provided information is: Although writers do not have fixed salaries, entrenched stereotyping results in a substantial pay gap between male and female authors. This sentence encapsulates the core issues presented in the text, including the disparity in advances paid to male versus female authors, the pricing and royalty differences, the tendency for male authors to win more literary awards, and receive more speaking invitations.
These factors collectively contribute to the income inequality experienced by female authors in the publishing industry. By highlighting 'entrenched stereotyping,' the sentence also hints at broader systemic issues that extend beyond individual cases.