Yes, better understanding of the stack makes you a more efficient prompt engineer. and yes I don't say this ironically, prompt engineering / vibe coding is not easy, as evidenced by the amount of people who think it's only good greenfield yeet prototypes.

A lot of my programming skills have atrophied over the last two years, and a lot of skills have become that much sharper (architecture, algorithm and design pattern knowledge, designing user facing tools and dev tools, setting up complex infrastructures, frontend design, ...) because they are what allow me to fly with LLMs.