Your quotation talks about design, not about looks. Huge difference.

Regardless, absolutely NO ONE who uses an application gives a shit about how it is implemented. All people see is the interface.

That may include elements that depend on implementation to make it responsive, but what matters is how it looks and feels to the user (i.e. fast). How that is achieved is irrelevant.

How it looks isn't "more important", it's the only thing that matters. All implementation changes are driven by design concerns.