Don't be stupid, if an AI can figure out how to arrange code, it can also figure out how to pick the right architecture choices.
Right now millions of developers are providing tons of architecture questions and answers. That's all going to be used as training data for the next model coming out in 6 months time.
This is a moat on our jobs as deep as a puddle.
If you believe LLMs will be able to do complex coding tasks, you must also concede they will be able to make the relatively simpler architecture choices easily simply by asking the right questions. Something they're already starting to be able to do.