For the purposes of chess the domain knowledge is the game rules. And from this pov there is really not much to describe, knowing en-passant exists is the peak of domain knowledge.
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.
I don't know how you can say application and experience isn't domain knowledge. If it isn't, I have no idea wtf we are talking about and I'll have to accuse you of moving goalposts.
You use websites a lot.
Should AI make you really good at frontend development?
Infinitely better than I was before it, yes. If not, what's the point?
I will answer my question as you answered a different one:
No, you do not become a really good FE dev from having used websites with AI in the mix.
Why should chess be different?