For example, I used to do integrations for sports betting sites. AI is going to help with the basics, like understanding the default puck line is 1.5 in hockey. AI is not going to realize that Bet365 changes their API endpoints for each season, so you need to be ready to fetch the updated ones before the new season starts, whereas most other sportbooks have consistent endpoints that you don't need to keep updating.
How much domain knowledge is actually unavailable to AI is going to vary by domain, as will the value of that. Chess is probably one extreme, where all knowledge is public, whereas something like military R&D might be the other extreme where domain knowledge is tightly guarded.
The other things you describe, such as endgame tables, are really more related to the domain of chess-computing, a subdomain of algorithms, and likely something you exceed your friend's knowledge in.
Getting to a high rank in chess isn't about better domain knowledge, is about application and experience.