An LLM can absolutely do the harder stuff too. I wonder what model you have used where you think it's only for the easy stuff.
Of course you need understanding for when shit hits the fan, but that applies regardless of whether it's a human or an LLM writing the code.
We've had the best people using the best and most expensive models. They confidently produce shit they thought they understood but didn't.
LLMs remove personal exploration from tasks and that's where you really get to know things.