With an AI assistant, in the best scenario, you'll get a "wisdom of crowds" effect on implementation details and program architecture. At worst, you'll get a lot of opinionated code bloat and anti-patterns as suggestions.
For most backend programming jobs, the challenge is not in writing complex code but figuring out what the business wants, needs and should have in the first place and distinguishing between them. Figuring out how to integrate with existing systems, processes, fiefdoms and code. Knowing when to say yes and no, how to make code future proof, etc. This is a task fundamentally unfit for what we currently call "AI", because it's not actually intelligent or creative yet.
On the frontend, it becomes even more nebulous. Maybe Copilot can suggest common themes like Bootstrap classes for a form, CSS properties, the basic file structure and implementations for components in an SPA, etc. As I see it, the main challenge is in UX there, not the boilerplate, which again makes it about understanding the user, figuring out how to make UI feel intuitive, etc. Again: unfit for current AI.
I cannot offer any opinion on the utility for actually complex, FANG-level code, for lack of experience.