I'm not sure if this is a comment written out of naivety of the profit focused nature of studios or ignorance of the writing process. Replacing writers and paying writers less is effectively the same thing. That "full credit" that you mention isn't just about what those writers got paid, it tells you what work they did.

For example, a writer will often write a treatment of a movie which is effectively a short summary of a movie that is done before writing a script. Sometimes different writers will do the treatment and screenplay. This is generally the distinction you might see in "Story By" and "Written By" credits in movies (although these distinctions can and often are a lot more complicated). One likely goal of the studios is for an AI to write the treatment and then hand that off to a writer to turn it into a screenplay. That is one of the most practical ways AI can be used since treatments aren't an end product themselves and the AI's flaws can be corrected by humans when translating the treatment into a script. However, that is still effectively replacing writers by taking away one of their clearly defined jobs and in turn one of their paychecks.