Huh? What are you talking about? Marketing is the job of Marketers, which in most companies (certainly small to mid companies) includes the content on the marketing web-page.
>You’d think that at some level the ‘faster websites sell more’ speech gets through to them
The technical aspect of how a web-site works, or how it is deployed or how quickly it is rendered, is NOT their job. Optimizing render speed of a given web-page is not part of their skillset - nor should it be. There are folks who specialize in that, typically software engineers. It is also not reasonable to expect marketing folks to create html/css/javascript and deploy via git. You really do want those folks to be independent and create the necessary content without needing an engineer anytime they want to add a new sub-section or fix a spelling mistake.
One "problem" is that most small/mid size businesses are not willing to hire technical folks or use engineering resources to do the technical part of this work. Another problem is that there should not be a tension between ease-of-use by editor and page rendering speed. Maybe WP is a bad product, and if so, what is the alternative that covers both use cases?
