It's about division of labor, and having clear interfaces between teams. If you are a one-person project, then by all means go that route. But in a team with specialized talent in backend and frontend development, both are much more efficient when that separation exists. Expecting frontend devs to write efficient SQL queries is about as insane as expecting a backend dev to know how to make complex CSS animations.
I said front end devs, not designers. And that is literally called out as a specific proposed benefit in the article.
And I don't know what to tell you, absolutely no one is advocating for JSP style SQL-inlined-in-HTML or something.
This just isn't a problem for most modern stacks. You're using an ORM and not writing SQL which isn't any harder than GraphQL or Rest endpoints.
And, for better or worse, there's not that much need to write efficient SQL because servers are so fast these days. The target you need to hit is something like "one of my filter conditions has an index" and things will usually be fine.