The only studies I'm aware of used tiny samples and produced muddled conclusions. If you have some conclusive empirical research then do feel free to share it though. Meanwhile, using LLMs doesn't mean doing less, it just means focusing on different things. The skill deficit here is the same kind as the skill deficit people have using punch cards or writing assembly by hand today. As more aspects of coding become automated, different things become relevant and that's what people shift their attention to.