the job description of a junior engineer can change. junior engineers can use AI to make themselves more productive too
"Productive junior" is vastly different than a productive software developer with a couple decades of experience. What they produce will differ in quality significantly, AI or no AI.
In my experience, AI raises the ceiling but also lowers the floor. It can make experienced people more productive: they can vet the output. The juniors? Not so much. I've worked with guys who write prompts that are literally "fix it." The result is about as good as you expect.