Firstly there is the double edged sword of AI when learning. The easy path is to use it as a way to shortcut learning, to get the juice without the pressing, skipping the discomfort of not knowing how to do something. But that's obviously skipping the learning too. The discomfort is necessary. On the flip side, if one uses an llm as a mentor who has all the time in the world for you, you can converse with it to get a deeper understanding, to get feedback, to unearth unknown unknowns etc. So there is an opportunity for the wise and motivated to get accelerated learning if they can avoid the temptation of a crutch.
The less tractable problem is hiring. Why does a company hire junior devs? Because there is a certain proportion of work which doesn't take as much experience and would waste more senior developers time. If AI takes away the lower skill tasks previously assigned to juniors, companies will be less inclined to pay for them.
Of course if nobody invests in juniors, where will the mid and senior developers of tomorrow come from? But that's a tragedy of the commons situation, few companies will wish to invest in developers who are likely to move on before they reap the rewards.