I think you're right, but I think the motivation for a lot of posts like this are rooted in developers working with designers who believe "issues like which UI containers should be scaled on what rules (full-screen or safe area? hugging the screen outside or inside?) for different screen sizes" should be within their domain of influence.

That separation of responsibilities is always a tough line to define in reality, and I do agree that the tools used by whomever is assuming that role should become more like developer tools.