If your goal is to prove what an awesome writer you are, sure, avoid AI.

If your goal is to just get something done and off your plate, have the AI do it.

If your goal is to create something great, give your vision the best possible expression - use the AI judiciously to explore your ideas, to suggest possibilities, to teach you as it learns from you.

Personally, as a DM of casual games with friends, 90% of the fun for me is the act of communal storytelling. That fun is that both me and my players come to the table with their own ideas for their character and the world, and we all flesh out the story at the table.

If I found out a player had come to the table with an LLM generated character, I would feel a pretty big betrayal of trust. It doesn't matter to me how "good" or "polished" their ideas are, what matters is that they are their own.

Similarly, I would be betraying my players by using an LLM to generate content for our shared game. I'm not just an officiant of rules, I'm participating in shared storytelling.

I'm sure there are people who play DnD for reasons other than storytelling, and I'm totally fine with that. But for storytelling in particular, I think LLM content is a terrible idea.

LLMs have issues with creative tasks that might not be obvious for light users.

Using them for an RPG campaign could work if the bar is low and it's the first couple of times you use it. But after a while, you start to identify repeated patterns and guard rails.

The weights of the models are static. It's always predicting what the best association is between the input prompt and whatever tokens its spitting out with some minor variance due to the probabilistic nature. Humans can reflect on what they've done previously and then deliberately de-emphasize an old concept because its stale, but LLMs aren't able to. The LLM is going to give you a bog standard Gemini/ChatGPT output, which, for a creative task, is a serious defect.

Personally, I've spent a lot of time testing the capabilities of LLMs for RP and storytelling, and have concluded I'd rather have a mediocre human than the best LLMs available today.