User manuals were great. However, they can get outdated. They're expensive. They're not earth-friendly. Once you're done reading and know a game - they wind up in my user manual closet.
But they were all we had.
Now - with advanced in AI - I think online useful tutorials and such will quickly be far better than user manuals ever were.
Whether a physical user manual or an online AI-based tutorial - it's only as useful as the information given. Sometimes tutorials are written by the game wizards because they're the experts. However, being an expert doesn't always translate into being able to effectively communicate to non-experts.
I always had the expert write the manual/help file and then have a non-expert (me) read it and see where certain points could be better clarified.