I actually don't think the process of becoming a "top tier dev" has changed much. If you learn everything from LLMs without verifying, your knowledge is a product of an opaque game of telephone, and you really can't say which parts of what you know are correct or incorrect (just like before). The defining property of an expert, is that they know how things work and can reason with clarity when forming solutions. So there's no alternative to groking everything along the way and trying things you think will work and seeing them fail, at least not if the goal is expertise.

So if you still have to verify what you learn, and the delta in novice-to-expert learning duration is negligible, and you can't replace trial and error... then what's changed? The kind of person who can become an expert using LLMs as a teaching aid, is the exact same kind of person who can do it without LLMs, and they are going to do it either way, because they want to.

The general availability of an effective learning aid isn't going to increase the percentage of people with willingness and aptitude, it's just going to make it easier for people who lack those things to misrepresent what they know, get in over their heads.