Rather that avoiding delegating it to LLM for these tasks helps you practice that skill.

That said, I think it depends how you use it. You can learn from explanations, and you'd better avoid "rewrite this for me and do nothing else" kind of approach.

Right, but the LLM can help you practice the skill too. Without the LLM, you're in a self-guided, autodidactical mode. Obviously, that can have its own advantages, but most people—but especially novices—aren't in a position to assess their skill level or their progress. The average person isn't going to magically get better at thinking or writing without formal training, or at least some direction.