What skills are atrophying that would be useful in the future?

If you're letting LLMs do more than assisting, don't. That's my advice. But if like you're title they're just assisting you, then what skills are atrophying? You still review the code and understand it right? You still second guess the LLMs proposed solutions and look for better approaches right?

Articulating how LLM assistance is different than junior programmers writing code and assisting would be useful, everyone has different setups and workflows, so it's hard to say in my opinion.